问题 单项选择题

可水解马拉硫磷的酶是().

A.环氧化物水化酶

B.羧基肽酶

C.氨基肽酶

D.羧酸酯酶

E.芳香酯酶

答案

参考答案:D

解析:马拉硫磷在高等动物体内和昆虫体内的代谢过程不同,在高等动物体内,马拉硫磷首先被肝中的羧酸酯酶水解为一羧酸和二羧酸而失去毒性。但是在昆虫体内,则发生氧化作用,成为毒力更高的马拉氧磷,从而发挥杀虫作用。

单项选择题
阅读理解

阅读理解。

     The need to feed a growing population is putting much pressure on the world's supply of water. With

97% of the world's water too salty to be drunk or used in agriculture, the worldwide supply of water needs

careful management, especially in agriculture.

     Although the idea of a water shortage seems strange to someone fortunate enough to live in a high rainfall

country, many of the world's agricultural industries experience constant water shortages. Although dams

can be built to store water for agricultural use in dry areas and dry seasons, the costs of water redistribution

(重新分配) are very high. Not only is there the cost of the engineering itself, but there is also an environmental

cost to be considered. Where valleys are flooded to create dams, houses are lost and wildlife homes destroyed.

Besides, water may flow easily through pipes to fields, but it cannot be transported from one side of the world

to the other. Each country must therefore rely on the management of its own water to supply its farming

requirements.

     This is particularly troubling for countries with agricultural industries in areas dependent on irrigation. In

Texas, farmers' overuse of irrigation water has resulted in a 25% reduction of the water stores. In the Central

Valley area of southwestern USA, a huge water engineering project provided water for farming in dry valleys,

but much of the water use has been poorly managed.

     Saudi Arabia's attempts to grow wheat in desert areas have seen the pumping of huge quantities of

irrigation water from underground reserves. Because there is no rainfall in these areas, such reserves can only

decrease, and it is believed that fifty years of pumping will see them run dry.

1. From the first two paragraphs we learn that _______.

A. much of the world's water is available for use

B. people in high rainfall countries feel lucky

C. water can be easily carried through pipes across the world

D. the costs of water redistribution should be considered .

2. Which of the following is true?

A. The underground water in Saudi Arabia might run out in 50 years.

B. Most industries in the world suffer from water shortages.

C. The water stores in Texas have been reduced by 75%.

D. Good management of water use resulted from the project in the Central Valley.

3. The text is mainly about _______.

A. water supply and increasing population

B. water redistribution and wildlife protection

C. water use management and agriculture

D. water shortages and environmental protection

4. What is most likely to be discussed in the paragraph that follows?

A. Approaches to handling the pressure on water supply.

B. Ways to reduce the costs of building dams.

C. Measures to deal with worldwide water shortages.

D. Steps to improving water use management