问题 问答题 简答题

园艺作物品种混杂退化的原因是什么?如何防止其退化?

答案

参考答案:

(1).混杂退化的原因①机械混杂②生物学混杂③不重视选择,缺乏选择制度而造成的退化④留种株数过少而造成的退化⑤自然条件、栽培条件不适当而造成的退化。(2).防止退化的原因①防止机械混杂②防止生物学混③重视选择,健全选择制度④留种株数超过100株防治退化⑤创造最适合的自然条件、栽培条件防治退化。

单项选择题 A1型题
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Last August, Joe and Mary Mahoney began looking at colleges for their 17-year-old daughter, Maureen. With a checklist of criteria (衡量标准)in hand, the Dallas family looked around the country visiting half a dozen schools. They sought a university that offered the teenager’s intended major, one located near a large city, and a campus where their daughter would be safe.

“The safety issue is a big one,” says Joe Mahoney, who quickly discovered he wasn’t alone in his worries. On campus tours other parents voiced similar concerns, and the same question was always asked: what about crime? But when college officials always gave the same answer -----“That’s not a problem here,”-----Mahoney began to feel uneasy.

“No crime whatever?” comments Mahoney today. “I just don’t buy it.” Nor should he: in 1999 the U.S. Department of education had reports of nearly 400,000 serious crimes on or around our campuses. “Parents need to understand that times have changed since they went to college,” says David Nichols, author of Creating a Safe Campus. “Campus crime mirrors the rest of the nation.”

But getting accurate information isn’t easy. Colleges must report crime statistics(统计数字) by law, but some hold back for fear of bad publicity(关注), leaving the honest ones looking dangerous. “The truth may not always be serious,” warns S. Daniel Carter of Security on Campus, Inc., the nation’s leading campus safety watchdog group.

To help concerned parents, Carter promised to visit campuses and talk to experts around the country to find out major crime issues and effective solutions.

小题1:It is often difficult to get correct information on campus crime because some colleges ____.

A.receive too many visitors

B.mirror the rest of the nation

C.hide the truth of campus crime

D.have too many watchdog groups小题2:The underlined word “buy” in the third paragraph means _____.

A.mind

B.admit

C.believe

D.expect小题3: We learn from the text that “the honest ones” in the fourth paragraph most probably refers to colleges _____.

A.that are protected by campus security

B.that report campus crimes by law

C.that are free from campus crime

D.that enjoy very good publicity小题4:What is the text mainly about?

A.Exact campus crime statistics.

B.Crimes on or around campuses.

C.Effective solutions to campus crime.

D.Concerns about kids’ campus safety.