若3a2+mb3和(n﹣2)a4b3是同类项,且它们的和为0,则mn的值是( ) A.﹣2 B.﹣1 C.2 D.1 答案:A【解答】解:由3a2+mb3和(n﹣2)a4b3是同类项,得 2+m=4,解得m=2. 由它们的和为0,得 3a4b3+(n﹣2)a4b3=(n﹣2+3)a4b3=0,解得n=﹣1. mn=﹣2,When _____ comes to codes of ethics, I think everyone should strictly obey them.A.thatB.thisC.itD.one