问题 选择题

已知直线l,a,b,平面α,β,下列命题正确的是(  )

A.若l⊥a,l⊥b,且a,b⊂α,则l⊥α

B.若a⊥α,b⊥a,则bα

C.若αβ,a⊥β,则a⊥α

D.若α⊥β,a⊥β,则aα

答案

由题意

A选项不正确,由线面垂直的判定定理知,一条直线垂直于平面中的两条相交直线时,线与面垂直,本题不能保证a,b,故不正确;

B选项不正确,由线面位置关系得,一条直线垂直于一个平面的垂线,此线与面的关系是线面平行或者线在面内,故不正确;

C选项正确,因为一条直线垂直于两个平行平面中的一个,必垂直于另一个,故命题正确;

D选项不正确,因为一条直线与一个平面都垂直于同一个平面,此面与线的位置关系是线在面内或线与面平行.

综上,C选项正确

故选C

完形填空

阅读下面短文并回答问题,然后将答案写到题后的横线上(请注意题后的词数要求)。

[1]Some people's ears produce wax like busy little bees. This can be a problem even though earwax appears to serve an important purpose. Experts say it protects and cleans the ear. It traps dirt and other matter and keeps insects out. Doctors think it might also help protect against infections. And the waxy oil keeps ears from getting too dry.

[2]So earwax is good. It even has a medical name: cerumen. And there are two kinds. Most people of European or African ancestry have the "wet" kind: thick and sticky. East Asians commonly have ___________.But you can have too much of a good thing.

[3]The glands(腺体) in the ear canal that produce the wax make too much in some people. Earwax normally falls out of the ear or gets washed away. But extra wax can harden and form a blockage that interferes with sound waves and reduces hearing. People can also cause a blockage when they try to clean out their ears,but only push the wax deeper inside. Earwax removal is sometimes necessary. But you have to use a safe method or you could do a lot of damage.

[4]Experts at N.I.H., the National Institutes of Health, suggest some ways to treat excessive earwax yourself. One way to remove wax is known as irrigation. With the head upright, take hold of the outer part of the ear. Gently pull upward to straighten the ear canal. Use an injector device to gently direct water against the wall of the ear canal. Then turn the head to the side to let the water out.

[5]The experts at N.I.H. say you may have to repeat this process a few times. Use water that is body temperature. If the water is cooler or warmer, it could make you feel dizzy. Never try irrigation if the eardrum is broken. It could lead to infection and other problems.

[6]After the earwax is gone, gently dry the ear. But if irrigation fails, the best thing to do is to go to a health care provider for professional assistance.

小题1:What’s the purpose of the passage? (No more than 10 words)

___________________________________________________________________.

小题2:What’s the bad effect of too much earwax on our hearing? (No more than 15 words)

____________________________________________________________________.

小题3:Fill in the blank in Paragraph 2 with proper words. (No more than 3 words)

____________________________________________________________________.

小题4:What does the underlined word “this process” (Line 1, Paragraph 5) probably refer to?

(No more than 2 words)

____________________________________________________________________.

小题5:Will you use freezing water when trying to remove earwax? Why or why not? 

(No more than 10 words)

____________________________________________________________________.

单项选择题