The biggest safety threat（威胁）facing airlines today may not be a man with a gun ,but the man with portable（便携式）computer in business class .In the past 15 years ,pilots have reported about over 100 incidents that could have been caused by electro-magnetic interference(电磁干扰) .The source of this interference remain unclear ,but increasingly ,experts are pointing the blame at portable electronic devices（设备）such as portable computers ,radio and mobile telephones .

RTCA ,an organization which advises the aviation industry ,has suggested that all airlines ban, such devices from being used during “key” stages of flight ,particularly take-off and landing .Some experts have gone further ,calling for a total ban during all flights .Nowadays ,rules on using these devices are left up to airlines. And although some airlines ban passengers from using such equipment during take-off and landing ,most are not willing to exercise a total ban ,if many passengers want to work during flights .

The difficulty is understanding how electromagnetic fields might affect an aircraft’s computers .Experts know that portable devices give off radiation which affects those wave lengths which aircraft uses for communication .But because they have not been able to reproduce these effects in a laboratory ,they have no way of knowing whether the interference might be dangerous or not .

The fact that aircraft may be in trouble because of the interference raises the danger

that some people may use radio systems in order to damage navigation（导航）equipment .As worrying ,though ,is the passenger who can’t hear the instruction to turn off his radio because the music is too loud .

1..

.What is said about over 100 aircraft incidents in the past 15 years ?

A They may have taken place during take-off and landing .

B They have been caused by the damage to the radio systems .

C They were said to have resulted from electro-magnetic interference .

D They were caused by the passengers’ portable computers .

2..

. Few airlines want to refuse a total ban on their passengers because ____ .

A they have other effective safety measures to fall back on

B they don’t believe there is such a danger as radio interference

C the effect of electromagnetic interference is yet to be proved

D most passengers refuse to take a plane which bans the use of radio 

3..

. Why is it difficult to see the effects of electromagnetic fields on computers ?

A Experts lack proper equipment to such research .

B It is dangerous to carry out such research on an airplane .

C It remains a question what wave lengths are to be interfered with .

D Scientists are not able to produce the same effects in laboratory .

4..

 It can be inferred from the passage that the author ___ .

A hasn’t formed his own opinion on this problem

B has fully understood the danger of electromagnetic interference

C regards it is as unreasonable to exercise a total ban during flight

D is in favor of banning passengers’ use of electronic devices

 

Don’t mention that at the beginning of the story, or it may ____ the shocking ending.

   A. give away      B. give out      C. give up        D. give off

 

Electric cars will not be really much cleaner than autos powered by mineral fuels until they rely less on electricity produced from usual coal-fired power plants.

 “For electric vehicles to become a major green alternative, the power fuel has to move away from

coal, or cleaner coal technologies have to be developed,” said Jared Cohon, the chairman of a National

Research Council report released on Monday. About half of US power is produced by

burning coal, which gives off many times more of traditional pollutants than natural gas, and about

twice as much of the main greenhouse gas carbon dioxide. Nuclear and renewable power have to

generate a larger portion of US power for electric cars to become much greener compared to

gasoline-powered cars, Cohan, who is president of Carnegie Mellon University, said in an interview.

Advances in coal burning, like capturing carbon at power plants for permanent burial underground,

could also help electric cars become a cleaner alternative to vehicles powered by fossil fuels, he said.

Pollution from energy sources did $120 billion worth of damage to human health, agriculture and

recreation in 2008, and electricity was responsible for more than half of the damage, said the NRC

report.

  Electric cars have their benefits such as reducing imports of foreign oil. But they also have hidden

costs. Materials in electric car batteries are hard to produce, which adds to the energy it takes to make

them. In fact, the health and environmental costs of making electric cars can be 20 percent greater

than usual cars, the report said.

  The report estimated that electric cars could still cost more than gas-powered cars to operate and

manufacture in 2030 unless US power production becomes cleaner.[来源:]

1. Why are electric cars not clean enough?

   A. Because they run too slowly              B. Because they are too expensive

   C. Because they rely on coal-fired power.      D. Because they give off more carbon dioxide.

2. We can infer from the passage that ______.

   A. electric cars will soon take the place of gas-powered cars

   B. no one holds hope for electric cars at present

   C. electric cars waste more energy than before

   D. some people believe that electric cars are cleaner

3. The underlined word “them” refers to “______”.

   A. electric cars     B. batteries       C. producers        D. materials

4. Which of the following is NOT mentioned as a way to make electric cars cleaner?

   A. Developing cleaner coal technologies.        B. Making electric cars run faster.

   C. Generating more unclear power.             D. Making advances in coal burning.

 

The manager of the company told us that was their final decision and that we had to _________.

A．give in

B．give off

C．give back

D．give away