通读下面短文，掌握其大意，然后在各小题所给的四个选项中，选出一个最佳答案，并将其字母编号写在题号前的括号内。

Long, long ago, there were great cities in many places in North Africa．But they are not there any　 46　 ．At that time there were gardens and trees and grass. But now these places are like　 47　 . Scientists began to study this land to 　48 　what had happened．Many of them believe the land died when the trees were 　49　

　　 Trees help _ 50　 　plants to grow. Tree roots hold the soil in place. They try to make the soil　 51 　in one place. In forests, leaves on the ground 　52　 　rainwater. Trees near farms protect growing plants when a strong 　53　 　comes.

Now, we try to 　54　 　trees. In many forests, when a tree is cut down, a new tree is planted in its place. We don't want the land 　55　 ．

46．(　　 )A．long　　　 　　　 B．longer　　 　　　 C．longest　　 　　 D．the longest

47．(　　 )A．deserts　 　　　　　　　 B．forests　　　 　 C．fields　　 　　　 D．hills

48．(　　 )A．look for　　 　　 B．find out　　　 C．look out　　 　　 D．take out

49．(　　 )A．grown　　 　　 B．cut down　　 　 C．watered　　 　 D．looked after

50．(　　 )A．another　　 　　 B．the other　　 　 C．other　　　 　　 D．others

51．(　　 )A．run　　　 　　 B．stay　　　 　　　 C．carry　　　 　　 D．leave

52．( 　　)A．dry　　　 　　 B．keep　　　　 　 C．drink　　　 　 D．have

53．(　　 )A．wind　　　 　 B．rain　　　 　　 C．snow　　　 　　 D．man

54．(　　 )A．cut　　 　　　　 B．water　　　 　　 C．save　　　　 　 D．study

55．(　　 )A．living　　 　　　 B．to live　　 　　 C．dying　　　 　 D．to die

45．(　　 )--Bob, you won the boys' 400 meters race. Congratulations.

　　　　 --_________

A．Where　　　　　 B．That's nothing　 　　 C．What a pity　　　 　 D．Thanks a lot

44．(　　 )Things would be much better if he ______to hospital a little earlier.

　 　 A．go　　　　　　 　 B．goes　　　　　　 C．went　　　　 　　　 D．will go

43．(　　 )--Is Mr. Smith speaking?

　　　　　 --This is David．My father _________ Singapore on business.

A．has been to　　　 　 B．has gone to　　　 　 C．has been in　　　 D．has come to

42．(　　 )There is nothing important in today's newspaper, ________?

　　　 A．isn't there　　　 　 B．is it　　　　　　 　 C．isn't it　　　　　 　 D．is there