A:CH4和CH3(CH2)2CH3
B:CH3CH3和CH3CH2CH3
C:CH2=CH2和CH2=CHCH3
D:CH3(CH2)2CH3和CH3CH(CH3)CH3
如图所示,用AO、BO绳吊一重物P静止,其中AO绳水平.现用水平向右的力F缓慢拉起重物P的过程中,绳OB所受的拉力变化为( )
— Does he have a soccer ball?
— _______. But he has two ping- pong bats.