题目

—Did you see Mr Black just now? —Yes. He ________ his car when I met him. A．parked                                           B．was parking C．parks                                            D．will park 答案：B有关命题的说法有下列命题：①若p∧q为假命题，则p、q均为假命题②“x=1”是“x2-3x+2=0”的充分不必要条件③命题“若x2-3x+2=0则x=1”的逆否命题为：“若x≠1，则x2-3x+2≠0”④对于命题p：?x∈R，使得x2+x+1＜0，则¬p：?x∈R，均有x2+x+1≥0其中所有正确结论的序号是    ．