燃料的热值单位是____或____。
若ab>0,则一定有( )
如图所示,人静止在水平地面上的测力计上,下列说法正确的是( )
提示:be strict with…… shout at …… be busy with …… less time ……
Would you mind ……?
Dear father,
I'm very happy to be your son, but sometimes……
Yours son