A growing number of students spend so much time on internet and TV with less and less rest and study, which _______ parents and educators very much.

A．settles

B．conquers

C．concerns

D．commands

根据研究对象的不同，力学分支包括（）。

A.固体力学

B.流体（包括液体和气体）力学

C.一般力学

D.运动力学