设随机变量X满足两点分布,P(X=1)=p,P(X=0)=q,其中p+q=1,则D(X)为( )
A:p
B:q
C:pq
D:p+q
下列合并同类项正确的是( )
-Is there ____ bread in the fridge?
-Yes. Would you like _________?
计算:23﹣233+563.