I can't find my way in the street . I don't know _____________.
A:what to do it
B:where to go
C:how to do it
D:which to do it
重为500N的物体放在水平地面上,与地面的滑动摩擦因数为μ=0.2,在大小为F=500N,方向与水平面成α=37°斜向上的拉力作用下前进l=10m,(sin37°=0.6,cos37°=0.8)在此过程中力F做功为( )
关于人体氨基酸的叙述,正确的是( )