如图,在Rt△ABC中,∠ACB=90°,CD⊥AB,垂足为D.若AC=2,BC=1,则sin∠ACD=( )
A:53
B:255
C:52
D:23
填空题。
地球是人类的家园.读经纬网图,对各地描述不可信的是( )
While her mother was cooking, she ____ ____ ____ a good idea.
— Mr Zhang really has a great sense of __________.
— Yeah. He often makes us laugh.