From this story we can learn: sometimes things done out of will may be _______.

A．people use too many man-made materials
B．the pupulation of the world is increasing faster
C．we are producing more cars, trucks and buses
D．we have more and more industry

A．As industry is growing fast, pollution is the natural result.
B．It's time we did something to reduce pollution.
C．We should control the speed of the development to stop pollution.
D．With the development of technology, pollution has become a serious problem.