群落演替的总趋势是 A.物种多样性的增加和种群稳定性的提高 B.物种多样性的减少和群落稳定性的降低 C.物种多样性的增加和群落稳定性的降低 D.
某地运用新技术、新工艺对传统产业进行改造,开发出优质、高效、符合消费者需求的新产品,使这些产业重新焕发生机和活力。这说明( ) A.传
The largest television network in America is not ABC, CBS, or Fox.Nor is it one of the cable net—works such as CNN, which carries only news and news stories.It is not ESPN, the all-sports cable
34.中国古代,“天”被尊为最高神。秦汉以后,以“天子”自居的皇帝举行祭天大典,表明自己“承天”而“子民”,官员、百姓则祭拜自己的祖先。
(5分)反射是在神经系统参与下,机体对内、外环境变化作出的应答。有人做了脊蛙反射实验,请分析并回答下列问题: (1)实验前须将蛙头部剪去
一物体以一定的初速度,沿倾角可在0—90°之间任意调整的木板向上滑动,设它沿木板向上能达到的最大位移为x。若木板倾角不同时对应的最大位移x与
一首歌中唱道“让我告诉世界,中国命运自己主宰,让我告诉未来,中国进行着接力赛……”你知道中国人民“命运自己主宰”开始于 A.1949
Most people feel lonely sometimes, but it usually only lasts a few minutes or a few hours. This kind of loneliness is not serious. In fact, it is quite normal. For some people, though, loneliness can