日日人人_亚洲美女在线视频_av手机在线播放_国产大片aaa_欧美中文日韩_午夜理伦三级

The research is so designed that once _______ nothing can be done to change it.

A. begins B. having begun

C. beginning   D. begun

D


解析:

D。由于 the research 與 begin 是被動關系，故用過去分詞 begun。Once begun 可視為 once it is begun 之省略。

練習冊系列答案
相關習題

科目：高中英語 來源：皇冠優(yōu)化名題　高中英語 題型：050

　　Sweet potatoes are fat-free,high in fiber and full of the vitamins that research suggests reduce your risk of life-shortening diseases．To stay healthy,we must eat more fruits and vegetables,and sweet potatoes are a great source of beta carotene（胡蘿卜素）and other carotenoids．According to a study of the diets of almost 90,000 nurses,eating about one cup a day of fruils and vegetables rich in carotenoids(which the body turns into vitamin A)can cut your risk of stroke in halt and reduce your risk of heart disease by 22 percent．Other resear chsuggests beta carotene protects against breast,lung and stomach cancers．

　　Beta carotene is the most famous member of the carotenoids family．In fact,a medium sized sweet potato contains nearly 12 mg of beta carotene(antiaging experts usually suggest 6 to 11 mg perday)．Sweet potatoes are also a low-fat source of vitamin E．Research has linked high E diets with a lower risk of heart disease．This vitamin pill in an orange jacket also packs a vitamin C punch-it has more C than apricots(a kind of fruit)．Research suggests that vitamin C protects against ailments ranging from cataracts(an eye disease)to cancer．In addition,A UCLA(University of California,Los Angels)study linked high vitamin C diets with a longer life．Recent studies have showed that antioxidant vitamins C,E and beta carotene fight a fierce battle against free radicals（自由基）,which cause cell（細胞）damage and lead to various illnesses．Therefore,to keep fit,eat more sweet potatoes．

(1)

According to the text,there exists a lot of ________ in sweet potatoes．

[　　]

A．

fiber,beta carotene,other earotenoids,vitamin E and C

B．

beta carotene,other carotenoids,fiber,vitamin A and E

C．

vitamin A,beta carotene,fiber,vitamin E and C

D．

beta carotent,other carotenoids,vitamin A and E

(2)

This text as a whole suggests that eating sweet potatoes can help ________

[　　]

A．

cut your risk of stroke and heart disease

B．

protect against breast,lung and stomach cancers

C．

protect against ailments ranging from cataracts to cancer

D．

you stay healthy and reduce your risk of life shortening diseases

(3)

“This vitamin pill in an orange jacket”in the passage refers to ________

[　　]

A．

sweet potato

B．

vitamin C pill

C．

vitamin E pill

D．

beta carotene

(4)

The best title of this passage might be ________

[　　]

A．

The Vitamin Superstar

B．

On Sweet Potatoes

C．

Beta Carotene and Vitamins

D．

Diet and Disease

查看答案和解析>>

科目：高中英語 來源： 題型：053

閱讀理解： 　　

閱讀下面短文，從所給四個選項中，選出最佳答案。

　Can trees talk? Yes——but not in words． Scientists have reason to believe that trees do communicate (互通信息) with each other． Not long ago, resear- chers learned some surprising things． First a willow tree(柳樹)attacked in the woods by caterpillars(毛毛蟲)changed the chemistry of its leaves and made them taste so terrible that the caterpillars got tired of the leaves and stopped eating them． Then even more astonishing, the tree sent out a special vapour — a signal causing its neighbours to change the chemistry of their own leaves and make them less tasty．

　　　Communication, of course, doesn't need to be always in words． We can talk to each other by smiling, raising our shoulders and moving our hands． We know that birds and animals use a whole vocabulary of songs, sounds, and movements． Bees dance their signals, flying in certain patterns that tell other bees where to find nectar(花蜜)for honey． So why shouldn't trees have ways of sending messages?

1． When attacked, a willow tree will protect itself by________．

[　　]

A． changing its leaves’chemistry

B． changing its leaves’colour

C． talking to caterpillars

D． sending a special vapour

2． From the passage we know that catrpillars________．

[　　]

A． like willow trees

B． enjoy eating fallen leaves

C． feed on willow tree leaves

D． could communicate with willow trees

3． Caterpillars will stop eating willow tree leaves which________．

[　　]

A． have a chemical change and become tasteless

B． have a pleasant taste

C． are being attacked

D． are communicating

4． According to the passage, how do willow trees communicate with each other?

[　　]

A． They talk in words．

B． They send out a special vapour．

C． They wave their leaves．

D． They make special sounds．

5． According to the passage, bees communicate with each other by______．

[　　]

A． talking

B． making unusual sounds

C． singing songs

D． fly in certain patterns

查看答案和解析>>

同步練習冊答案
主站蜘蛛池模板： 国产精品久久久久一区二区三区 | 精品乱码一区二区 | 亚洲视频 欧美视频 | 精品久久久久久久 | 亚洲一区二区三区 | www.日| 毛片网络| 亚洲欧美一区二区三区在线 | 日韩黄色小视频 | 久久三区 | 在线播放国产一区二区三区 | 国产精品久久久久久免费一级 | 久久亚洲欧美日韩精品专区 | 欧美一级特 | 日韩一区二区在线播放 | 国产精品a久久久久 | 在线欧美视频 | 黄色网址免费在线观看 | 色婷婷亚洲国产女人的天堂 | 日韩av免费在线观看 | 在线亚洲观看 | 欧美精品久久久 | 精品亚洲一区二区三区 | 日本免费一区二区三区 | 日本a视频 | 精品在线播放 | 超碰人人99 | 国产精品热| 国产亚洲tv | 国产a一三三四区电影 | 日韩一区二区在线观看 | 欧美在线综合 | 四虎国产精品成人免费影视 | 国产精品成人一区二区三区夜夜夜 | 日韩一区二区电影 | 在线欧美视频 | 日韩中文字幕一区 | 日韩福利在线观看 | 在线视频一二三 | 成人a在线| 日本在线视频一区二区三区 |