问题 选择题

在光学显微镜下可以观察到的结构是

A.人口腔上皮细胞的细胞壁

B.草履虫体内的叶绿体

C.烟草花叶病毒的蛋白质外壳

D.黄瓜表层果肉细胞的叶绿体

答案

答案:D

题目分析:植物细胞与动物细胞的相同点:都有细胞膜、细胞质、细胞核;植物细胞与动物细胞的不同点:植物细胞具有细胞壁、叶绿体和液泡,动物细胞不具有细胞壁、液泡、叶绿体.

A、人口腔上皮细胞没有细胞壁;

B、草履虫是动物,其细胞内没有叶绿体;

C、烟草花叶病毒只有在电子显微镜下才能看到;

D、黄瓜表层果肉细胞有叶绿体,并且可以在光学显微镜下观察到.

单项选择题

My Space and other Web sites have unleashed a potent new phenomenon of social networking in cyberspace, (1) at the same time, a growing body of evidence is suggesting that traditional social (2) play a surprisingly powerful and under-recognized role in influencing how people behave.

The latest research comes from Dr. Nicholas A. Christakis, at the Harvard Medical School, and Dr. James H. Fowler, at the University of California at San Diego. The (3) reported last summer that obesity appeared to (4) from one person to another (5) social networks, almost like a virus or a fad. In a follow-up to that provocative research, the team has produced (6) findings about another major health (7) : smoking. In a study published last week in the New England Journal of Medicine, the team found that a person’s decision to (8) the habit is ply affected by (9) other people in their social network quit—even people they do not know. And, surprisingly, entire networks of smokers appear to quit virtually (10)

For (11) of their studies, they (12) of detailed records kept between 1971 and 2003 about 5,124 people who participated in the landmark Framingham Heart Study. Because many of the subjects had ties to the Boston suburb of Framingham, Mass. , many of the participants were (13) somehow—through spouses, neighbors, friends, co-workers—enabling the researchers to study a network that (14) 12,067 people.

Taken together, these studies are (15) a growing recognition that many behaviors are (16) by social networks in (17) that have not been fully understood. And (18) may be possible, the researchers say, to harness the power of these networks for many (19) , such as encouraging safe sex, getting more people to exercise or even (20) crime.

10()

A.surprisingly

B.simultaneously

C.spontaneously

D.ply

单项选择题 B型题