较为陌生的人相交谈宜使用( )
A.亲密距离
B.个人距离
C.社交距离
D.公共距离
参考答案:C
I'm afraid there _______________ a heavy rain tonight. [ ]
A. will have
B. is going
C. will be
D. is going to have
设X,y是两个随机变量,则下列不正确的是()。
A、cov(X,Y)=cov(Y,X)
B、cov(X,X)=D(X)
C、cov(X,Y)=E[(X-E(X))(Y-E(Y))]
D、cov(X,Y)=E(XY)-E(X)E(Y)