题目内容
x∈A∩B.则x∈A_______x∈B.
选用“或”“且”“非”填空,使下列命题成为真命题:
x∈A∪B.则x∈A_______x∈B.
若ab=0,则a=0_______b=0.
a、b∈R且a>0_______b>0,则ab>0.