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(1)若AB，則A∩B＝A.

(2)若A∪B＝B，則AB.

(3)（A∩B）A（A∪B）.

(4) _U（A∩B）＝（_UA）∪（_UB）.

__________________________

A.a＜3                                                            B.a≥－2

C.a≥－3                                                         D.－2≤a＜3

①ABA∪B=B  ②A∪B=BA∩B=A  ③A∪B=B∪CA=C  ④A∪B=I?(_IA)∩(_IB)=   ⑤A∩B= (_IA)∪(_IB)=I

A.2                                                                 B.3

C.4                                                                 D.5

A.4                                                                 B.3

C.2                                                                 D.1

A.B                                                                 B.A

C.                                                              D.Z

A.A={1，8}，B={2，6}

B.A={1，3，5，8}，B={2，3，5，6}

C.A={1，8}，B={2，3，5，6}

D.A={1，3，8}，B={2，5，6}