下列说法正确的是（　　）

A．任何物体在磁场的作用下都会产生磁性

B．磁感线是磁体发出的实际曲线

C．磁场是客观存在的，磁感线是假想的曲线

D．地球的南北极与地磁场的南北极方向一致

Which of the following would be a likely theme for the next paragraph

A．Naturally changing ecological conditions.

B．Animals that have become extinct.

C．Achievements of the government Endangered Species Program.

D．Programs that have destroyed natural habitats.