下列物质中,只含共价键的是( ) A. B. C. D.

题型:选择题

问题:

下列物质中,只含共价键的是(  )

A.

B.

C.

D.

考点:化学键与化学反应中能量变化的关系
题型:选择题

按照IMF《国际收支手册》的界定,以下机构属于美国居民的有( )

A.联合国

B.中国驻美大使馆

C.哈佛大学

D.国际货币基金组织

E.美国驻华大使馆

题型:选择题
选择适当的单词填空完成短文。
      Mary comes 1___________ Australia. She is twelve. She is in China 2___________ her family now. She
is a student. She 3___________ her school and her classmates. She speaks Chinese, but she 4___________
speak Chinese very well. Mary gets up very early 5___________ the morning. She has milk and bread
6___________ breakfast. Then she goes to school by bike. In the evening she does her homework and reads
books. She 7___________ to bed 8___________ 9: 00. She is very 9___________ every day.
( ) 1. A. in
( ) 2. A. with
( ) 3. A. likes
( ) 4. A. don't
( ) 5. A. on
( ) 6. A. in
( ) 7. A. go
( ) 8. A. in
( ) 9. A. happy
B. from
B. and
B. like
B. isn't
B. in
B. from     
B. goes
B. at
B. bad
C. for
C. or
C. is likes
C. doesn't
C. for
C. for
C. going
C. for
C. well
题型:选择题

患者于某,女性,68岁。癫病日久不愈,神思恍惚,魂梦颠倒,心悸易惊,善悲欲哭,肢体困乏,饮食锐减,言语无序,舌淡,苔薄白,脉沉细无力。其辨证分型是()

A.痰火内扰证

B.心脾两虚证

C.痰气郁结证

D.火盛伤阴证

E.心火扰动证

题型:选择题

SQL SELECT语句中的WHERE子句对应于查询设计器中的( )。

A. “字段”选项卡

B. “筛选”选项卡

C. “排序依据”选项卡

D. “分组依据”选项卡

题型:选择题

A bite of a cookie containing peanuts could cause the airway to constrict fatally. Sharing a toy with another child who had earlier eaten a peanut butter and jelly sandwich could raise a case of hives. A peanut butter cup dropped in a Halloween bag could contaminate the rest of the treats, posing an unknown risk.

These are the scenarios that "make your bone marrow turn cold" according to L. Val Giddings, vice president for food and agriculture of the Biotechnology Industry Organization. Besides representing the policy interests of food biotech companies in Washington, D. C., Giddings is the father of a four-year-old boy with a severe peanut allergy. Peanuts are only one of the most allergenic foods; estimates of the number of people who experience a reaction to the beans hover around 2 percent of the population.

Giddings says that peanuts are only one of several foods that biotechnologists are altering genetically in an attempt to eliminate the proteins that do great harm to some people’s immune systems. Although soy allergies do not usually cause life-threatening reactions, the scientists are also targeting soybeans, which can be found in two thirds of all manufactured food, making the supermarket a minefield for people allergic to soy. Biotechnologists are focusing on wheat, too, and might soon expand their research to the rest of the "big eight" allergy-inducing foods: tree nuts, milk, eggs, shellfish and fish.

Last September, for example, Anthony J. Kinney, a crop genetics researcher at DuPont Experimental Station in Wilmington, Del., and his colleagues reported using a technique called RNA interference (RNAi) to silence the genes that encode p34, a protein responsible for causing 65 percent of all soybean allergies. RNAi exploits the mechanism that cells use to protect themselves against foreign genetic material; it causes a cell to destroy RNA transcribed from a given gene, effectively turning off the gene.

Whether the public will accept food genetically modified to be low-allergen is still unknown. Courtney Chabot Dreyer, a spokesperson for Pioneer Hi-Bred International, a subsidiary of DuPont, says that the company will conduct studies to determine whether a promising market exists for low allergen soy before developing the seeds for sale to farmers. She estimates that Pioneer Hi-Bred is seven years away from commercializing the altered soybeans.

Doug Gurian-Sherman, scientific director of the biotechnology project at the Center for Science in the Public Interest—a group that has advocated enhanced Food and Drug Administration oversight for genetically modified foods—comments that his organization would not oppose low-allergen foods if they prove to be safe. But he wonders about "identity preservation" a term used in the food industry to describe the deliberate separation of genetically engineered and no nengineered products. A batch of nonengineered peanuts or soybeans might contaminate machinery reserved for low-allergen versions, he suggests, reducing the benefit of the gene-altered food. Such issues of identity preservation could make low-allergen genetically modified foods too costly to produce, Chabot Dreyer admits. But, she says, "it’s still too early to see if that’s true. \

According to the text, foods have been genetically altered to()

A. taste more delicious

B. to cure people’s ineffectiveness in immune system

C. to promote sales of peanut

D. to lower the chance to get allergy

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