问题 选择题 下列各式:2x3,-a,a2b,3a+b,0,-5x2y,7x-y2中,是单项式的个数为( )A.2个B.3个C.4个D.5个 答案 所给式子中单项式有:2x3,-a,0,-5x2y,共4个.故选C.