问题 问答题 简答题

简述果树无性繁殖的优点及种类?

答案

参考答案:

(1)果树绝大多数是多年生木本植物,优良品种的特性只能通过无性繁殖才能得以遗传,无性繁殖较有性繁殖有如下优点:无性繁殖可以保持亲本的优良性状不被改变;无性繁殖可以使果树的结果提前,不经过童期;无性繁殖可以加快新优品种的推广速度。

(2)果树无性繁殖的种类:扦插、压条、分株和嫁接,其中嫁接和扦插在果树繁殖中最常见。

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 is not easy, even hopeless.

“We have many children left to place—40 out of 75,” said Straub, who works for a Paris-based foreigner-exchange program started 50 years ago. Family life was more than accommodating (提供膳宿). For one thing, more mothers stayed at home. But now, increasing numbers of women work outside the home. Exchange-student programs have struggled in recent years to sign up host (主人) families for the 30 000 teenagers who every year come from abroad to spend a school year in the United States, as well as the thousands more who take part in summer programs.

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

In search for host families, who usually receive no pay, exchange programs are increasingly broadening their requests to include everyone from young couples to retirees.

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

For elderly people, exchange students “keep us young—they really do”, said Jen Foster, who is hosting 16-year-old Nina Post from Denmark.

小题1:The underlined word “exotic” means _________.

A.difficult

B.wonderful

C.exciting

D.accommodating小题2:According to the text, why was it easier for Laura Straub to find American families for foreign students?

A.More mothers wasn’t working outside and was able to afford to look after children .

B.American school systems were better than now.

C.Foreign students paid hosting families a lot of money.

D.The government was happy because it could gain tax.小题3:Which of the following statements is true according to the passage?

A.All the families can host foreign students.

B.Only young couples can host foreign students.

C.Only those who were retired can host foreign students.

D.Exchange programs are open to many different types of families including everyone from young couples to retirees.小题4:Which of the following is the best title of this passage?

A.U.S. Struggle 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