设随机变量X
i
～
【正确答案】
A
【答案解析】解析：由题意得 P(X
1
=一1，X
2
=一1)=P(X
1
=一1，X
2
=1) =P(X
1
=1，X
2
=一1)=P(X
1
=1，X
2
=1)=0 P(X
1
=一1，X
2
=0)=P(X
1
=一1)=
，P(X
1
=1，X
2
=0)=P(X
1
=1)=
， P(X
1
=0，X
2
=一1)=P(X
2
=一1)=
，P(X
1
=0，X
2
=1)=P(X
2
=1)=
，P(X
1
=1，X
2
=0)=P(X
1
=1)=
， P(X
1
=0，X
2
=一1)=P(X
2
=一1)=
，P(X
1
=0，X
2
=1)=P(X
2
=1)=