题干

大多数细胞的直径不到0.01cm,细胞之所以体积小原因是(  )

A:有利于物质交换和通讯

B:代谢旺盛

C:生活力强

D:细胞分裂快

上一题 下一题 0.0难度 选择题 更新时间:2017-11-19 10:52:46

答案(点此获取答案解析)

A

同类题1

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,选项中有两项为多余选项。

    Eyesight plays avery important role in our daily life. Every waking moment, the eyes are working to see the world around us. Over forty percent of Americans worry about losing eyesight, but it's easy to include steps into our daily life to ensure healthy eyes. Here are five suggestions for a lifetime of healthy eyesight:

    •Schedule yearly exams.____Experts advise parents to bring babies 6 to 12 months of age to the doctor for a careful check. The good news is that millions of children now can have yearly eye exams and following treatment, including eyeglasses.

    •Protect against UV rays(紫外线).Long­term stay in the sun creates risk to your eyes. No matter what the season is, it's extremely important to wear sunglasses.____

    •Give your eyes a break. Two­thirds of Americans spend up to seven hours a day using computers or other digital products.____ Experts recommend that people practice the 20/20/20 rule: every 20 minutes, take a 20­second break and look at something 20 feet away.

    •____As part of a healthy diet, eat more fruits and vegetables each day. Vitamins(维生素) C and E help protect eyesight and promote eye health.

    •Practice safe wear and care of contact lenses(隐形眼镜).Many Americans use contact lenses to improve their eyesight. While some follow the medical guidance for wearing contact lenses, many are breaking the rules and putting their eyesight at risk.____ Otherwise, you may have problems such as red eyes, pain in the eyes, or a more serious condition.

A.Eat your greens.

B.Eye care should begin early in life.

C.They can properly protect your eyes.

D.Stay in good shape by taking more Vitamins.

E.Parents usually don't care about their own eyesight.

F.Always follow the doctor's advice for appropriate wear.

G.This frequent eye activity increases the risk for eye tiredness.