ComboBox项目突出显示xaml windows phone 8.1中的2项

Question

我正在使用带有40个项目的组合框，它将在弹出窗口中打开，选择项目后弹出窗口关闭，如果我尝试选择不同的项目，弹出窗口会突出显示2个项目以及一个我没有选择的项目。我尝试改变风格，但它对我不起作用。

 <ComboBox >
                <ComboBoxItem>
                    <TextBlock Text="One"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="Two"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="Three"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Four"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Five"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Six"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Seven"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Eight"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Nine"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Ten"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="Eleven"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="Twelve"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="Thirteen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Fourteen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Fifteen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Sixteen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Seventeen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Eighteen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Nineteen"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Twenty"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentyOne"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="TwentyTwo"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="TwentyThree"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentyFour"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentyFive"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentySix"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentySeven"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentyEight"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="TwentyNine"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Thirty"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtyOne"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="ThirtyTwo"/>
                </ComboBoxItem>
                <ComboBoxItem>
                    <TextBlock Text="ThirtyThree"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtyFour"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtyFive"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtySix"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtySeven"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtyEight"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="ThirtyNine"/>
                </ComboBoxItem>

                <ComboBoxItem>
                    <TextBlock Text="Fourty"/>
                </ComboBoxItem>
            </ComboBox> 

提前致谢：）