某人用照相机给一位同学先拍了张全身像，现在改为拍半身像，他应该（　　）

A．靠近该同学，同时把镜头前伸

B．远离该同学，同时把镜头前伸

C．靠近该同学，同时把镜头后缩

D．远离该同学，同时把镜头后缩

Cumulus clouds that have undergone vertical development and have become cumulonimbus in form，indicate（）.

A.clearing weather

B.that a warm front has passed

C.probable thunderstorm activity

D.an approaching hurricane or typhoon