人们在岸上二行走的脚步声能把水中的鱼吓跑,这是因为鱼能听到下列哪种介质传来的声音? ( )
A:空气
B:土地
C:水
D:土地和水
His sister always comes here ________ eight ________ the morning.
The mother is worried ________ her son's study.