Study harder______
A.if you will pass the exam
B.and you pass the exam
C.unless you pass the exam
D.or you won‘t pass the exam

Potential dehydration is______ that a land animal faces.
A.the often greatest hazard
B.the greatest often hazard
C.often the greatest hazard
D.often the hazard greatest

______the students here are serious about studying.
A.Most
B.Almost
C.Almost of
D.Most of

You will not succeed_______ working harder.
A.unless
B.if
C.without
D.although

You _____the washing up. l could have done it to you
A.hadn't to do
B.needn’t have done
C.couldn’t have done
D.mustn’t have done

(46)
A.use
B.used
C.to use
D.using

(48)
A.it
B.they
C.there
D.those

According to the passage, which of the following is the most important cause of desertification?
A.The change of climate
B.The spread of deserts
C.Human activities
D.Cattle destroying trees

When all the trees in an area are cut down, _________.
A.their leaves make the land richer
B.the smaller plants can grow better
C.they cool the land under their leaves
D.there is nothing left but sand

We can infer that men on motorcycles keep the sheep and goats away so that_________.
A.they won't eat the small trees
B.they won't destroy the covering of oil
C.they won't drink water in the canals
D.they won't blow the sand away