A:unique
B:separate
C:single
D:alternative
下列流行语中,属于20 世纪80年代的有
放在水平地面上重为300N的箱子,小明用200N的力来抬它,则箱子受到的合力为____ N.
You don't know ______ I want to see you again. It's a year since I last saw you.