氨气分子的空间构型为三角锥形,而甲烷则是正四面体形,这是因为( )A.NH3分子中有一对未成键的孤对电子,而甲烷的4个sp3杂化轨道全部形成σ键
---Is Mary still performing? ----I’m afraid not. She is said_____ the stage already. A. to have left B. to leave C. to have been left D. to be left
the end of last term, every student in the school, I think, has taken at least five maths tests. A. By B. Since C. From D. In
73.《诗经》是我国第一部诗歌总集,《诗经》里面包括多少首诗?( ) A.三百首B.三百零五首
—You see, I’m poor in maths, you are not good at English, and... — That’s ____ we should help each other. A.when B.where
阅读下面的文言文,完成后面题目。 战国策目录序 曾巩 刘向所定《战国策》三十三篇,《崇文总目》称第十一篇者阙。臣访之士大夫家,始尽得其
下列几幅图片代表的是当今世界一些重要的国际组织,它们共同反映了( ) A.经济全球化的发展趋势 B.欧洲国家联合起来反
将一个细胞中的磷脂成分全部提取出来,将其在空气-水界面上铺成单分子层,结果测得单分子层的表面积相当于原来细胞膜表面积的两倍。下列细胞实