<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="" Width="">

    <Grid>

        <Grid.RowDefinitions>

            <RowDefinition Height=""/>

            <RowDefinition Height="*"/>

        </Grid.RowDefinitions>

        <StackPanel Grid.Row="" Orientation="Horizontal" FocusManager.IsFocusScope="True">

            <ComboBox Width="">

                <ComboBoxItem></ComboBoxItem>

                <ComboBoxItem></ComboBoxItem>

                <ComboBoxItem></ComboBoxItem>

            </ComboBox>

            <ComboBox Width="">

                <ComboBoxItem>a</ComboBoxItem>

                <ComboBoxItem>b</ComboBoxItem>

                <ComboBoxItem>c</ComboBoxItem>

            </ComboBox>

        </StackPanel>

        <RichTextBox Grid.Row=""/>

    </Grid>

</Window>