直接上图，有真相。。。
接下来是XAML代码：
<Window x:Name="DNF连发" x:Class="DNF连发.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="DNF连发" Height="350" Width="535" Closed="DNF连发_Closed" Loaded="DNF连发_Loaded" >
    <Grid x:Name="连发">
        <Border BorderBrush="Black" BorderThickness="1" HorizontalAlignment="Left" Height="4" Margin="135,169,0,0" VerticalAlignment="Top" Width="3"/>
        <ComboBox x:Name="下拉框1" SelectedValuePath="Tag" HorizontalAlignment="Left" Margin="64,34,0,0" VerticalAlignment="Top" Width="120" >
            <ComboBoxItem Name="选项1" Content="A" Tag="test1" Selected="选项Selected_1"></ComboBoxItem>
            <ComboBoxItem  Content="S" Tag="test2" ></ComboBoxItem>
            <ComboBoxItem  Content="D" Tag="test3" ></ComboBoxItem>
            <ComboBoxItem  Content="Z" Tag="test4" ></ComboBoxItem>
            <ComboBoxItem  Content="X" Tag="test5" ></ComboBoxItem>
            <ComboBoxItem  Content="C" Tag="test6" ></ComboBoxItem>
            <ComboBoxItem  Content="F" Tag="test7" ></ComboBoxItem>
            <ComboBoxItem  Content="G" Tag="test8" ></ComboBoxItem>
//</ComboBox>试过在这里加代码，可是报错。
            <ComboBox x:Name="下拉框2" SelectedValuePath="Tag" HorizontalAlignment="Left" Margin="64,102,0,0" VerticalAlignment="Top" Width="120"/>
            <ComboBoxItem  Content="A" Tag="test1" ></ComboBoxItem>
            <ComboBoxItem  Content="S" Tag="test2" ></ComboBoxItem>
            <ComboBoxItem  Content="D" Tag="test3" ></ComboBoxItem>
            <ComboBoxItem  Content="Z" Tag="test4" ></ComboBoxItem>
            <ComboBoxItem  Content="X" Tag="test5" ></ComboBoxItem>
            <ComboBoxItem  Content="C" Tag="test6" ></ComboBoxItem>
            <ComboBoxItem  Content="F" Tag="test7" ></ComboBoxItem>
            <ComboBoxItem  Content="G" Tag="test8" ></ComboBoxItem>
        </ComboBox>
        <ComboBox x:Name="下拉框3" HorizontalAlignment="Left" Margin="64,169,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框4" HorizontalAlignment="Left" Margin="64,232,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框5" HorizontalAlignment="Left" Margin="338,34,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框6" HorizontalAlignment="Left" Margin="338,102,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框7" HorizontalAlignment="Left" Margin="338,169,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框8" HorizontalAlignment="Left" Margin="338,232,0,0" VerticalAlignment="Top" Width="120"/>
        
        <Button x:Name="确定" Content="确定" HorizontalAlignment="Left" Margin="135,273,0,0" VerticalAlignment="Top" Width="75" Click="确定_Click" />
        <Button x:Name="重置" Content="重置" HorizontalAlignment="Left" Margin="300,273,0,0" VerticalAlignment="Top" Width="75" Click="重置_Click"/>
    </Grid>
</Window>

然后是CS文件：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace DNF连发
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        private void myComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
        }
        private void 重置_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("已重置，可以重新选择需要连发的按键！");
        }
        private void 确定_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("您已确定需要的连发按键吗？");
        }
        private void DNF连发_Closed(object sender, EventArgs e)
        {
            MessageBox.Show("谢谢使用，祝你生活愉快！");
        }
        private void DNF连发_Loaded(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("欢迎使用本软件");
        }
        private void 选项Selected_1(object sender, RoutedEventArgs e)
        {
         
        }
        private void ComboBoxItem_Selected_1(object sender, RoutedEventArgs e)
        {
        }
    }
}
需要的效果为，每个下拉框的选择项相同：

直接上图，有真相。。。
接下来是XAML代码：
<Window x:Name="DNF连发" x:Class="DNF连发.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="DNF连发" Height="350" Width="535" Closed="DNF连发_Closed" Loaded="DNF连发_Loaded" >
    <Grid x:Name="连发">
        <Border BorderBrush="Black" BorderThickness="1" HorizontalAlignment="Left" Height="4" Margin="135,169,0,0" VerticalAlignment="Top" Width="3"/>
        <ComboBox x:Name="下拉框1" SelectedValuePath="Tag" HorizontalAlignment="Left" Margin="64,34,0,0" VerticalAlignment="Top" Width="120" >
            <ComboBoxItem Name="选项1" Content="A" Tag="test1" Selected="选项Selected_1"></ComboBoxItem>
            <ComboBoxItem  Content="S" Tag="test2" ></ComboBoxItem>
            <ComboBoxItem  Content="D" Tag="test3" ></ComboBoxItem>
            <ComboBoxItem  Content="Z" Tag="test4" ></ComboBoxItem>
            <ComboBoxItem  Content="X" Tag="test5" ></ComboBoxItem>
            <ComboBoxItem  Content="C" Tag="test6" ></ComboBoxItem>
            <ComboBoxItem  Content="F" Tag="test7" ></ComboBoxItem>
            <ComboBoxItem  Content="G" Tag="test8" ></ComboBoxItem>
//</ComboBox>试过在这里加代码，可是报错。
            <ComboBox x:Name="下拉框2" SelectedValuePath="Tag" HorizontalAlignment="Left" Margin="64,102,0,0" VerticalAlignment="Top" Width="120"/>
            <ComboBoxItem  Content="A" Tag="test1" ></ComboBoxItem>
            <ComboBoxItem  Content="S" Tag="test2" ></ComboBoxItem>
            <ComboBoxItem  Content="D" Tag="test3" ></ComboBoxItem>
            <ComboBoxItem  Content="Z" Tag="test4" ></ComboBoxItem>
            <ComboBoxItem  Content="X" Tag="test5" ></ComboBoxItem>
            <ComboBoxItem  Content="C" Tag="test6" ></ComboBoxItem>
            <ComboBoxItem  Content="F" Tag="test7" ></ComboBoxItem>
            <ComboBoxItem  Content="G" Tag="test8" ></ComboBoxItem>
        </ComboBox>
        <ComboBox x:Name="下拉框3" HorizontalAlignment="Left" Margin="64,169,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框4" HorizontalAlignment="Left" Margin="64,232,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框5" HorizontalAlignment="Left" Margin="338,34,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框6" HorizontalAlignment="Left" Margin="338,102,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框7" HorizontalAlignment="Left" Margin="338,169,0,0" VerticalAlignment="Top" Width="120"/>
        <ComboBox x:Name="下拉框8" HorizontalAlignment="Left" Margin="338,232,0,0" VerticalAlignment="Top" Width="120"/>
        
        <Button x:Name="确定" Content="确定" HorizontalAlignment="Left" Margin="135,273,0,0" VerticalAlignment="Top" Width="75" Click="确定_Click" />
        <Button x:Name="重置" Content="重置" HorizontalAlignment="Left" Margin="300,273,0,0" VerticalAlignment="Top" Width="75" Click="重置_Click"/>
    </Grid>
</Window>

然后是CS文件：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
namespace DNF连发
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        private void myComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
        }
        private void 重置_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("已重置，可以重新选择需要连发的按键！");
        }
        private void 确定_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("您已确定需要的连发按键吗？");
        }
        private void DNF连发_Closed(object sender, EventArgs e)
        {
            MessageBox.Show("谢谢使用，祝你生活愉快！");
        }
        private void DNF连发_Loaded(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("欢迎使用本软件");
        }
        private void 选项Selected_1(object sender, RoutedEventArgs e)
        {
         
        }
        private void ComboBoxItem_Selected_1(object sender, RoutedEventArgs e)
        {
        }
    }
}
需要的效果为，每个下拉框的选择项相同：