The sun will burn you ______ you're not careful.

A．early man did not know how to make use of trees
B．tree are not as useful now as they were in the past
C．trees were more useful in the past than they are now
D．men have always found trees useful

A．useless soil
B．soil found under the earth
C．soil on the surface of the earth
D．dry soil which is found in the desert