4、(0,)B.(,1)C.(0,)D.(,1)[答案] C[解析] 由已知条件可得P(X=1)=p,P(X=2)=(1-p)p,P(X=3)=(1-p)2p+(1-p)3=(1-p)2,则E(X)=P(X=1)+2P(X=2)+3P(X=3)=p+2(1-p)p+3(1-p)2=p2-3p+3>1.75,解得p>或p<,又由p∈(0,1),可得p∈(0,),故应选C.6.已知随机变量ξ,η满足ξ=2η-1,且ξ~B(10,p),若E(ξ)=8,则D(η)=( )A.0.5B.0.8C.0.2D.0.4[答案] D