[单项选择]Because of the great speed of light, we see a lamp light up almost at the exact moment______.
A. we turn it on
B. when we turn on it
C. that we turn on it
D. which we turn it on

[单项选择]Because of the great speed of light, we see a lamp light up almost at the exact moment （）.
A. we turn it on
B. when we turn on it
C. that we turn on it
D. which we turn it on

[填空题]In light therapy, you just sit near a special lamp for _______________ every morning.

[单项选择]

All we have a clock located inside our brains. Similar to your bedside alarm clock, your internal clock runs on a 24-hour cycle. This cycle, called a circadian rhythm, helps control when you wake, when you eat and when you sleep.
Somewhere around puberty, something happens in the timing of the biological clock. The clock pushes forward, so adolescents and teenagers are unable to fall asleep as early as they used to. When your mother tells you it’s time for bed, your body may be pushing you to stay up for several hours more. And the light coming from your computer screen or TV could be pushing you to stay up even later.
This shift is natural for teenagers. But staying up very late and sleeping late can get your body’s clock out of sync with the cycle of light and dark. It can also make it hard to get out of bed in the morning and may bring other problems, too. Teenagers are put
A. it has a cycle of 24 hours
B. it controls when we wake, when we eat and when we sleep
C. it can alarm any time during 24 hours
D. it is a cycle also called circadian rhythm

[简答题]It is only when we cannot see perfectly that we realize how important our eyes are.

[判断题]Moller shines light on yogurt to see how the patterns vary with air bubble size.

[填空题]We can see with our

[单项选择]______ is the first software we see when we turn on the computer.
A. Word processor
B. Internet
C. Operating system
D. Application

[单项选择]

When we see well, we do not think about our eyes very often. (76) It is only when we cannot See perfectly that we realize how important our eyes are.
People who are near-sighted can only see things that are very close to their eyes. Everything else seems blurry (unclear). Many people who do a lot of work, such as writing, reading and sewing, become near-sighted.
People who are far-sighted suffer from just the opposite problem. They can see things that are far away, but they have difficulty in reading a book unless they hold it at arm’s length, lf they want to do much reading, they must get glasses, too.
Other people do not see clearly because their eyes are not exactly the right shape. They have what is called astigmatism (散光). This, too, can be corrected by glasses. Some people’s eyes become cloudy because of cataracts(白内障). Long ago these people often became blind. Now, however, it is possible to operate on the cataracts and remove them.
A. seeing at night
B. seeing objects far away
C. looking over a wide area
D. judging distances