题目

知全集U，集合A、B满足A∪B=U，那么下列条件中一定正确的是（  ）w.w.w.k.s.5.u.c.o.m       A．     B．     C．    D． 答案：CQinghai-Tibet Railway(青藏铁路) was completed last year. It is the __________ railway that connects Tibet with the other parts of ChinaA.firstB.secondC.thirdD.fourth