急性上消化道出血最常见的病因（）
A.溃疡病出血
B.应激性溃疡
C.食管静脉破裂出血
D.胃癌
E.胆道出血
参考答案：A
—Here are three books on history. Which one would you like to borrow?
—________. You see, I'm interested in geography these days. [ ]
A. All
B. None
C. Both
D. Each
比位能是指（）流体的位势能。
A.单位质量
B.单位重力
C.单位体积
D.单位摩尔
