Why does land become desert after all trees are cut down?

A. Because nothing remains on land except floods.
B. Because there are no longer trees to keep the rain and protect the top-soil.
C. Because too much rain sinks in and washes away the top-soil.
D. Because roots of the trees break up the soil.
A. Because nothing remains on land except floods.
B. Because there are no longer trees to keep the rain and protect the top-soil.
C. Because too much rain sinks in and washes away the top-soil.
D. Because roots of the trees break up the soil.

【答案】