溢流关井时，井底压力约等于（）之和。
A.静液压力
B.环空压耗
C.地面回压（套压）
D.立压
E.抽汲压力
参考答案：A, C
—Do you know Huang Ting well?
—Yes. She and I _____ friends since we met in Wuhan last summer.[ ]
A. have made
B. were
C. have been
D. become
设总体X服从参数为λ(λ＞0)的泊松分布，X1，X2…Xn(n≥2)为来自该总体的简单随机样本．则对于统计量
(A) ET1＞ET2，DT1＞DT2． (B) ET1＞ET2，DT1＜DT2． (C) ET1＜ET2，DT1＞DT2． (D) ET1＜ET2，DT1＜DT2．
