His wife, to whom he _____ for 20 years, died of cancer last Thursday. （ ）
A：had married
B：has been married
C：has married
D：had been married
A. door B .cake C. sleep D. under the tree E. bird
F.lunch box G. crayon H. window I. high jump J. book
在洋葱根尖成熟区表皮细胞中能正常完成的生理活动有 （ ）①合成RNA聚合酶 ②核DNA→核DNA ③mRNA→蛋白质 ④线粒体叶绿体的DNA复制 ⑤逆转录过程 ⑥氨基酸脱水缩合
下列供热方式，最有利于环境保护的是（ ）
人类的历史变迁、世界的激烈竞争、祖国的百年沧桑，已经无数次地证明：落后就要挨打。他时刻警示着我们（ ）
