Many scientists believe that global warming, if       , will cause extreme climate changes this century.

         A．not stopping         B．no stop             C．not stopped         D．without stop

Many scientists believe that global warming, if       , will cause extreme climate changes this century.

       A．not stopping        B．no stop           C．not stopped        D．without stop

Many scientists believe that global warming , if        , will cause extreme climate changes this century .

       A．not stopping    B．no stop     C．not stopped     D．without stop ycy

Many scientists believe that global warming，if ________ ，will cause extreme climate changes this century.

A. not stopping 　　　　　　　 B. not stop

C. not stopped 　　　　　　　 D. without stop

　　Terrible weather, melting (融化的) snow and gathering clouds may be signs of global warming．The average temperature on Earth for last year was the second warmest since written records began 140 years ago．

　　“The global average surface temperature in 2001 was 14．42 degrees centigrade,”the World Meteorological Organization (WMO世界气象组织) said．The record, set in 1998, was 14．58 degrees centigrade．

　　“Temperatures are getting hotter, and they are getting hotter faster now than at any time in the past,” said Michel Jarraud, a WMO official．

　　Carbon dioxide (二氧化碳) produced from burning fuels is the most common of the so-called greenhouse gases．The growing concentration (集中) in the atmosphere of these gases is thought to be warming the Earth．“Most of the causes of global warming are due to human action,” said Ken Davidson, director of WMO's climate programme department．

　　Every year, large amounts of gases produced by factories, cars and burning trees hold in too much heat and cause global warming．Many scientists believe the warming, if not stopped, will cause extreme climate changes this century．

　　Throughout the world, the spreading of particular diseases and other threats (威胁) to human health depend largely on local climates．Extreme temperatures can directly cause loss of life．Warm temperatures can increase air and water pollution, which in turn can harm human health．

　　In the Earth's atmosphere there are tiny amounts of gases called greenhouse gases．These gases hold in the heat that comes up from the sun-warmed Earth．As cities have increased in size and population, factories and industries in the world have grown．People need more and more electricity, cars and other things．So more greenhouse gases have been added to the atmosphere．This causes more heat to be trapped than in the past．This is called the greenhouse effect．

1．The subject discussed in the passage is________．

[　　]

A．the growing population of the world

B．the global average surface temperature

C．the increasing greenhouse effect

D．the causes of air and water pollution

2．According to a WMO official, it is________ that should be blamed for global warming．

[　　]

A．modern factories

B．human activities

C．carbon dioxide

D．burning fuels

3．The rising of the earth temperature will finally result in ________．

[　　]

A．the spreading of particular diseases

B．air and water pollution

C．extreme climate changes

D．all of the above

4．Which of the following is TRUE according to the passage?

[　　]

A．Air and water pollution is caused by global warming．

B．Greenhouse gases do no good to human beings．

C．With the air getting hotter, people need more and more electricity, cars and other things．

D．The average temperature on Earth for 1998 was the warmest according to written records．