手掌按住正在发声的鼓面,鼓声消失了,原因是手( )
A:不能传播声音
B:吸收了声波
C:把声音反射回去了
D:使鼓面停止了振动
With the loss of labor,the old farmers ________at home had to choose less laborintensive crops.
数一数,填一填,答一答。