DNA分子经过诱变，某位点上一个正常碱基（设为P）变成了尿嘧啶。该DNA连续复制两次

学生在教员指导下讨论力矩问题时，最好从下列哪个问题开始（）

A.力矩会对飞机产生影响么

B.力矩是怎样对飞机产生影响的

C.是力矩引起飞机转弯吗

Windows对话框由下面的对象组成（）。

A.最大化按钮

B.标题栏

C.帮助按钮

D.最小化按钮

E.下拉列表框

简述古典经济学的基本政策主张及理论缺陷。

The following questions present a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.

These questions test correctness and effectiveness of expression. In choosing your answer, follow the requirements of standard written English; that is, pay attention to grammar, choice of words, and sentence construction. Choose the answer that produces the most effective sentence; this answer should be clear and exact, without awkwardness, ambiguity, redundancy, or grammatical error.

Because a rockslide had blocked much of the passage, the spelunking team was not able of exploring the till extent of the cave.（）

A. the spelunking team was not able of exploring the full extent of

B. the full extent was not able to be explored by the spelunking team of

C. the spelunking team was unable in exploring, to its full extent,

D. therefore the spelunking team was unable to explore the full extent of

E. the spelunking team was unable to explore the full extent of