We haven't seen ______ her sister ______ her.

A．man has cut down too many trees
B．man is eager to profit from trees
C．man hasn't realizes the importance of trees to him
D．man hasn't found cut that he has lost all trees

A．keep rain from falling down to soft ground
B．cause the soil to allow rainwater to sink in
C．make the topsoil stick together
D．prevent the soil from being washed away