介质中质点产生相应的横向和纵向两种振动的合成，质点作椭圆轨迹的振动和传播称为（）。
参考答案：兰姆波
— I'm going to Hangzhou on vacation this weekend.
— Can you get some green tea for me ____ you are there. [ ]
A. if
B. after
C. while
D. as soon as
输送血液的泵是心脏．______．
