如图所示,静止在水平桌面上的木块,在水平方向受到推力F1、F2和摩擦力。已知 F1=10N,F2=2N,若撤去F1,木块在水平方向上受到的合力为( )
A:8N
B:2N
C:10N
D:0
Look at this desk. It's Jim's desk. It's brown. Jim's book is on it. The book is his English book. His pencil-box is on it, too. His pencil is in his pencil-box. But where's his pen? He can't find(找到) it.
①肺泡内的气体交换
②组织里的气体交换
③肺的通气
④气体在血液中的运输
—What club do you want to join, Han Mei?
— .
①H2SO3+I2+H2O═2HI+H2SO4
②2FeCl3+2HI═2FeCl2+2HCl+I2
③3FeCl2+4HNO3═2FeCl3+NO↑+2H2O+Fe(NO3)3.