6:下列代数式①-1,②-2/3a,③1/6x^2y,④:x+y/2⑤:ab/c⑥:3a+b⑦0⑧m中是单项式的是:
①③⑦⑧
7:单项式-2.1x10^2ab^c是(3+c)次单项式
8:单项式—2x^y/3的系数是(-2)次数是(y/3)