刚性防水层的振捣一般采用插入式振捣棒。
参考答案：错
A．声音的音调保持不变
B．声音的响度保持不变
C．声音的传播速度逐渐减小
D．以上说法都不对
We are tired of doing ________ homework every day; most of _______ is of no use but of
mechanical drill.
A．a lot of; it
B．the number of; which
C．a number of; it
D．a great deal of; which
