经过直线外一点,有几条直线和已知直线平行 ( )
A:0条
B:1条
C:2条
D:3条
如图所示,一束光由空气斜射入玻璃砖,画出这束光经过玻璃砖两个面折射的光路.
You can't watch TV until your homework is ____ (finish).