WPF之内容型控件（失败）

GroupBox

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <GroupBox Header="请选择年级" Height="205" HorizontalAlignment="Left" Margin="16,34,0,0" Name="groupBox1" VerticalAlignment="Top" Width="365">
            
            <StackPanel Height="162" Name="stackPanel1" Width="139" >
                <RadioButton Content="一年级"  Name="radioButton1" Margin="3" IsChecked="True" />
                <RadioButton Content="二年级"  Name="radioButton2" Margin="3" />
                <RadioButton Content="三年级"  Name="radioButton3" Margin="3" />
                <RadioButton Content="四年级"  Name="radioButton4" Margin="3" />
            </StackPanel>
        </GroupBox>
    </Grid>
</Window>

EXpand 单击按钮可以展开或隐藏控件内容 ScrollViewer控件自动显示滚动条（未实现）

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <ScrollViewer>
        <StackPanel Height="246" HorizontalAlignment="Left" Margin="8,13,0,0" Name="stackPanel1"  Width="479" >
            <Expander Header="本科生"  IsExpanded="True" HorizontalAlignment="Left" Margin="10,10,0,0" Name="expander1" >
                <StackPanel  Name="stackPanel2"  >
                    <RadioButton Content="一年级"  Name="radioButton1" Margin="3" IsChecked="True" />
                    <RadioButton Content="二年级"  Name="radioButton2" Margin="3" />
                    <RadioButton Content="三年级"  Name="radioButton3" Margin="3" />
                    <RadioButton Content="四年级"  Name="radioButton4" Margin="3" />
                </StackPanel>
            </Expander>
            <Expander Header="研究生"  IsExpanded="False" HorizontalAlignment="Left" Margin="10,10,0,0" Name="expander2" >
                <StackPanel  Name="stackPanel3"  >
                    <RadioButton Content="研1"   Margin="3" IsChecked="True" />
                    <RadioButton Content="研2"   Margin="3" />
                    <RadioButton Content="研3"  Margin="3" />
                    <RadioButton Content="研4"   Margin="3" />
                </StackPanel>
            </Expander>
            <Expander Header="研究生"  IsExpanded="False" HorizontalAlignment="Left" Margin="10,10,0,0" >
                <StackPanel    >
                    <RadioButton Content="研1"   Margin="3" IsChecked="True" />
                    <RadioButton Content="研2"   Margin="3" />
                    <RadioButton Content="研3"  Margin="3" />
                    <RadioButton Content="研4"   Margin="3" />
                </StackPanel>
            </Expander>
        </StackPanel>
    </ScrollViewer>
</Window>