How is your father? Please say hello to _____ for me. [ ]
A. she
B. him
C. it
D. her
答案:B
如图所示的玻璃砖为半径为R的半圆形玻璃砖上截取的一部分,其折射率为n,一束光线垂直于AB边入射,当人射点P距AB边中点至少为多远时,曲面上将无光线透射?
精液品质检查的直观指标有哪些?其意义是什么?