问题 选择题

下列光现象的成因与日食形成原因相同的是(  )

A.

水面“折”笔

B.

手影

C.

看露珠下的叶脉

D.

拱桥倒影

答案

日食的形成是月亮转到地球与太阳之间时,挡住了太阳射向地球的光线,是光的直线传播形成的,对照选项可进行分析判断.

A、看到斜插入水中的铅笔好像折断了,是光的折射现象,不符合题意;

B、手影的形成是光沿直线传播形成的现象,符合题意;

C、看露珠下的叶脉,叶脉变粗,是露珠起到了放大镜的作用,属光的折射,不符合题意;

D、平静的水面能形成岸上景物清晰的像,是利用了光的反射,不符合题意;

故选B.

选择题
阅读理解

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 .

小题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 .

小题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 

小题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 .

小题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