下列有3个自由度的关节是（）.
A.肘关节
B.膝关节
C.腕关节
D.肩关节
参考答案：B
—My teachers often encourage me ________ more friends but I find it difficult.
—Your teachers’ idea is right. The more friends you make, ________ you will be.
A．to make; the more happy
B．to make; happier
C．making; the happier
D．to make; the happier
咏叹调
