—Better not, dear. Never ___________ what you can do today till tomorrow.
A:put on
B:put out
C:put off
D:put up
在研究光的折射规律时,小明让一束激光沿白纸板照射,把手指头放于S点时刚好接收到红色的亮点. 然后将玻璃砖放于白纸板上,激光经玻璃砖向右侧照射,如图所示.他将手指头放于哪一点才可能接受到红色的亮点( )
当肋间肌和膈肌收缩时,气体经过的途径是( )