DNA是以半保留方式进行复制的，如果放射性全标记的双链DNA分子在无放射性标记的溶液中经两次复制，那么所产生的4个DNA分子其放射性状况如何？()
A. 两个分子含有放射性
B. 全部含有放射性
C. 双链中各有一半含有放射性
D. 所有分子的两条链都没有放射性
查看答案
How would you describe the writer's attitude toward Karaoke？
A. She often goes, and likes it sometimes and sometimes not.
B. She thinks it is not only fun, but stress relieving as well.
C. She has not tried it herself so has no attitude about it.
D. She feels it is a waste of tim
Why did the author's aunt try to teach her children to speak Korean？
A. To help her improve her Korean language skills.
B. To help them establish a Korean identity.
C. To help them succeed in the U. S.
D. To help them find a good jo
下列关于酶催化反应机理的方面的描述中，不正确的是()。
A. 底物和酶的临近效应与定向效应与催化有关
B. 共价催化与催化有关
C. 底物形变和诱导契合与催化有关
D. 酸碱催化与催化无关
Adders are most likely to be found______.
A. in shady fields in England
B. on uncultivated land throughout Britain
C. in Scotland and nowhere else
D. in wilder parts of Britain and Ireland
微信支付 
支付宝支付