题干

下列有关受精作用的叙述,正确的是(  )

A:受精卵中全部的遗传物质一半来自父方,一半来自母方

B:受精时,精子和卵细胞的染色体会发生联会现象

C:通常受精卵中的染色体数与本物种体细胞的染色体数相同

D:受精作用的最重要意义是保证了细胞核大小的稳定

上一题 下一题 0.0难度 选择题 更新时间:2012-08-17 02:10:53

答案(点此获取答案解析)

C

同类题4



   It's the end of class. When the bell rings, students of Luohu ForeignLanguages School in Shenzhen quickly take out their cell phones.
They want to log on to their micro blogs to check the interesting things that have happened in the last hour.
   Since last year, the trend (潮流) of micro blogging has swept the country. Recent surveys shows that most students in middle schools have a micro blog and some even update their blogs over five times per day.
   "We learn many fresh and interesting things on micro blogs and they have become popular topics in class," said Andy Liang, 14. "If you do not know about them, you are out of the loop."
   It is also a great place for students to let out stress. "My parents always ask me to study hard, and encourage me before exams, but it really adds pressure," said Simon Zhang, 15. "When I share these feelings on my micro blog, I get many replies from friends in the same situation, which makes me feel better."
   But parents are worried that micro blogging could be a waste of time. Some misleading messages may even cause danger to kids, they said.
   Mr. Shen, a professor at the China Education Association, suggests parents not worry too much as long as kids are not crazy about micro blogging. Maybe it can become a window for parents to understand their children.
   "If parents can read their children's micro blogs, they'll know their thoughts, thus leading to better communication and solutions to problems," he said. He also gives some tips for kids.
   -Don't micro blog for more than one hour a day.
   -Never micro blog in class.
   -Try to talk face to face with people from time to time.
   -Be critical(批判性的). Don't trust all the messages on a micro blog.