下列说法正确的是

A．磁感线是真实存在的，磁场由无数条磁感线组成

B．在地磁场作用下能自由转动的小磁针，静止时N极指向北

C．磁体外部的磁感线总是从S 极出发，回到N极

D．奥斯特实验表明，铜导线可以被磁化

The world’s population is growing ______ and there is _______ land and water for growing rice.

A．more; less

B．larger; fewer

C．larger; less

D．more; fewer