题目

--- How long        you       in the country with your grandparents, Henry?   --- About four weeks. I’ll return as soon as school starts.   A. are; staying    B. did; stay      C. do; stay           D. had; stayed   答案：A通过对《声现象》的学习，你认为下列说法中正确的是（　　）A．只要物体振动就一定能够听到声音B．“震耳欲聋”说明声音的音调很高C．在校园内植树可以减弱校外传来的噪声D．超声波的频率很低，所以人听不到