Of the sun’ s total output of radiant energy, the earth receives （）.

A．from mouth to mouth
B．from door to door
C．from the masses to the masses
D．from side to side

A．do not contribute to economic growth at all
B．are less useful to the society because they do not make direct contribution to economic growth
C．are similar to medical and social services in their way of promoting economic growth
D．should develop only when they are good for economic growth