近代有一位思想家主张学习西方，在其著作中提出了“物竞天择，适者生存”的观点。这位思想家是[ ]
A．詹天佑
B．严复
C．魏源
D．郭沫若
答案：B
There is a big library in our school.There are more than twice________five years ago. [ ]
A. books than
B. as many books as
C. many books as
D. many more books than
一个质量为m的小球从高处由静止释放，不计空气阻力，当小球下落高度h时，重力的瞬时功率为[ ]
A．
B．
C．
D．
