48. From the passage we learn that there are ________ ways to reserve soil.

A. only three　 　　　 B. two　　　　 C. more than three　　　 　　　 D. six

C

Africa is home to nearly 700 lakes and rivers. It holds the largest amount of water on earth. Because of the overuse of the lakes, natural climate changes and other factors(因素), these lakes are disappearing quickly.

Millions of people in Africa depend on water sources like lakes and rivers for their daily water. In other words, they cannot live without these lakes and rivers. Recent studies by the United Nations show that this loss of water supply is putting a great pressure on the African population.

In the 1960s, Lake Chad was nearly 83,200 square feet large. In about forty years, it has lost 95% of its size and it has almost completely dried up. At one time, it was one of the largest lakes in the world, and was around 960,000 square feet around 6,000 years ago.

The sizes of lakes and rivers and the amount of water have something to do with seasons naturally. But, pollution and agriculture also play an important part in the loss of water. Many pollutants(污染物)are put into lakes and rivers so that many lakes and rivers are seriously polluted, and the water may be poisonous(有毒的). If something isn’t done soon about the disappearing lakes and rivers, there will not be enough water for everyone. Then many people in Africa will face diseases and possible dehydration(脱水).

47. One way of soil conservation on flat, open ground is ________.

A. to grow small plants such as grasses　　　　 B. to plant trees around an open field

C. to add fertilizer to the soil　　　　　　　　 D. A and B

46. Plants cannot grow on eroded land because _____.

A. there is a lot of sand　　　　　　　　　　　 B. there is not enough water and salts

C. there is no water　　　　　　　　　　　　　 D. the land is too hard

45. On a rainy day the water running down the slopes of a hill is muddy because ________.

A. there is no terrace on the slopes　　　　　　 B. there is no small plant on the slopes

C. it washes away soil from the slopes　　　　　 D. there is too much soil on the slopes

44. What do you think of Iris?

A. Brave.　　　 　　 B. Kind.　　　 　　　 C. Honest. 　　　 D. Too careful.

B

On a rainy day, you will see many streams of muddy(多泥的)water running down the slopes(山坡)of a hill. The water is muddy because it washes away soil from the hill slopes.

Sometimes soil is blown away by strong winds. When the soil is carried away by water or wind, we say that the land is eroded(侵蚀). This is known as soil erosion.

Plants cannot grow on eroded land. There is not enough soil on eroded land to give them the things they need. Plants need water and salts from the soil.

We can do a number of things to stop soil erosion. This is called soil conservation(保护).

One way of soil conservation on flat, open ground is to grow small plants such as grasses. Their roots hold the soil tightly together. Another way is to plant trees around an open field. Thus soil erosion by strong winds cannot take place. Rows of trees act as a very big wall.

Soil erosion on slopes can be stopped by cutting “steps” called terraces(梯田). Water carrying soil cannot run straight down the slope now. It has to run down the terraces. This slows down the flow of the water. Most of the soil in the water is left behind on the terraces.

There are some other ways of soil conservation.

43. Which of the following is NOT mentioned in Iris’ worries?

A. Her electric cooker.　 　　　 B. Her baby.　　 C. Her key.　　 D. Her train.

42. Iris goes back to the kitchen to ________.

A. make sure that the cooker is off　　　　 B. turn off the cooker

C. feel the knob on the TV set　　　　　　 D. talk to someone

41. Iris worries too much because ________.

A. she usually forgets to turn off the cooker　　　 B. she usually forgets to turn off the TV set

C. she is very forgetful　　　　　　　　　　　 D. she usually forgets her key

39. A. jumped up 　　B. sat up　　　　　 　　C. rang up　　 　　　　D. knocked down