Without electricity, human life _____ quite different today. A. is B. will be C. would have been D. would be 答案:D已知四边形ABCD和对角线AC、BD,顺次连结各边中点得四边形MNPQ给出以下六个命题:①若所得四边形MNPQ为矩形,则原四边形ABCD是菱形 ②若所得四边形MNPQ为菱形,则原四边形ABCD是矩形 ③若所得四边形MNPQ为矩形,则AC⊥BD ④若所得四边形MNPQ为菱形,则AC=BD ⑤若所得四边形MNPQ为矩形,则∠BAD=90° ⑥若所得四边形MNPQ为菱形,则AB=AD
以上命题中,正确的是( )
A.①② B.③④
C.③④⑤⑥ D.①②③④