如图所示,小明同学一分钟完成了 20个“引体向上”,若小明同学每次“引体向上”重心上升约0.5m,则在此过程中小明同学克服重力做功的平均功率接近( )
A:1000W
B:100W
C:10W
D:1W
脊椎动物的进化历程是:鱼类→两栖类→爬行类→鸟类→哺乳类。(判断对错)
Has Daming got a letter from his mother ?(做肯定回答)
____ , he____ .
下列关于生态工程的叙述,错误的是( )
It's time _______ school.