轮齿分度圆及两啮合齿轮的节圆用()表示。
A．粗实线
B．细实线
C．点划线
D．虚线
参考答案：C
声压往复透射率在数值上与下列（）项相等。
A.声强反射率
B.声强透射率
C.声压透射率的平方
D.声压反射率的平方
As for how to promote public education, Professor Li gave us a lot of suggestions which _____ reasonable and practical.
A．appeared
B．sounded
C．looked
D．listened
