问题 单项选择题

Hb中一个亚基与其配体(O2)结合后,促使其构象发生变化,从而影响此寡聚体与另一亚基与配体的结合能力,此现象称为

A.协同效应
B.共价修饰
C.化学修饰
D.激活效应
E.别构效应

答案

参考答案:A

阅读理解

WASHINGTON—Laura Straub is a very worried woman. Her job is to find families for French teenagers who expect to live with American families in the summer.

It’s not easy, even desperate.

“We have many children left to place: 40 out of 75,” said Straub, who works for a Paris-based foreign exchange programme called LEC. When exchange programmes started 50 years ago, family life was more accommodating. For one thing, more mothers stayed home.

But now, increasing numbers of women work outside the home. Exchange-student programmes have struggled in recent years to sign up host families for the 30,000 teenagers who annually come from abroad to spend their academic year in the United States, as well as the thousands more who participate in summer programmes.

School systems in many parts of the US, unhappy about accepting non-taxpaying students, have also strictly limited the number of exchange students they accept. At the same time, the idea of hosting foreign students is becoming less exotic.

In searching for host families, who usually receive no pay, exchange programmes are increasingly broadening their appeals to include everyone who has the ability to do it.

“We are open to many different types of families,” said Vickie Weiner, eastern regional director for ASSE, a 25- year-old programme that sends about 30,000 teenagers on academic year exchange programmes worldwide.

“For elderly people, exchange students keep us young; they really do!” said Jean Foster, who is hosting 16-year-old Nina Porst from Denmark.

小题1:Vickie Weiner is the person who ________.

A.works for a programme called LEC

B.works for a programme called ASSE

C.is 25 years old

D.hosts foreign students小题2: From the passage we can learn that at the beginning of the exchange programmes_______.

A.all the families could host foreign students

B.only young couples could host foreign students

C.only those who were retired could host foreign students

D.those who were not too old could host foreign students小题3:Which of the following is the best title of this passage?

A.US Struggles to Find Host Families

B.Idea of Hosting Students Is Different

C.Foreign-exchange Program Is Going On

D.Exchange Students Keep Old People Young

单项选择题 A1/A2型题