题目内容：

The United Nations reports global warming is reducing rainfall and increasing temperatures in most of the world's deserts.A report suggests the changes are hurting many who farm on desert edges.

In West Africa, the effects are serious and making the food produced there not enough.Those living in farming regions along the Sahel desert have found their arable(适于耕种的) land is decreasing as desert sands cover more areas.The town of Podor once was a place where grains grew and cattle ate grass.But now, the people who live there say food is becoming harder and harder to get.The reason is the advancing desert.

Oumar Samba Kane is one of the leaders of his village.He carries a bag of grains from a neighbouring village to add to his village's nearly empty storeroom.“In the past years, we had enough food to last a year and we would sell the surplus(剩余) to make money，” Kane said.“Now we do not even have enough for ourselves.” Rivers once used for fishing and watering cattle are drying up.Pieces of green land are few and far between.Cows are basic food in the area, but now herders(牧人) must drive their cattle for days to look for grass.Crops have also suffered.And for the most part it is only older farmers, like Moussa Aliou Sow, who stay behind to try to do farm work.“I'm 67 years old，” Sow said, “All I know is agriculture.There is nothing else I can do.” He says his hands are tired of growing crops on the land, which is producing less and less.There used to be rice in these fields just a few years ago.

Scientists blame not only global warming, but also farming practices such as clearing trees and over planting crops for the desert's advance.But farmers say they can't survive without farming.

1.From the passage we know that global warming ____.

A. has reduced rainfall worldwide

B. has increased temperatures everywhere

C. has made the lives of many farmers on desert edges harder

D. has caused many deaths in West Africa

2.There isn't enough food in the town of Podor mainly because ____.

A. there are not enough farmers there

B. a lot of farming land has become desert

C. farmers are tired of growing crops on the land

D. a lot of farmland has been used to plant grass

3.What were things like in Oumar Samba Kane's village in the past？

A. The villagers had more than enough food to eat and could sell the rest for money.

B. The villagers had to borrow food from a neighbouring village.

C. Cattle couldn't get enough water because all rivers were dry.

D. Herders drove their cattle for days to find green land.

4.The passage mainly talks about ____.

A. villagers' life in West Africa

B. climate changes in the world

C. the development of farming

D. the effect of the advancing desert