阅读下面短文，从短文后所给的A、B、C、D四个选项中选出能填入相应空白处的最佳选项。

Dear Sally,

    How are you? I'm happy that you can do the things you 1 at home. I never have fun, because there are too many 2 in my family. My parents are strict. I have to 3 at six o'clock every morning. And I have to make my bed 4 before breakfast and then go to school. I can't play with my friends after school. I have to do 5homework. After dinner I have to take the dog for 6 walk in the park. I can't watch TV on school nights. I have to 7 the violin for an hour. I can't go to bed late. I have to be in bed 8 nine o'clock. On weekends I have to clean my room and 9the dishes. I also have to go to learn the violin on Sundays. I'm 10 tired. Can you help me?

Yours,

Lisa

如图，在长方体ABCD﹣A₁B₁C₁D₁中，AB=BC=2，AA₁=1，则BC₁与平面BB₁D₁D所成角的正弦值为（　　）