导致上消化道大量出血最常见的病因是（）
A.食管癌
B.胃癌
C.急性胃炎
D.消化性溃疡
E.肝硬化
参考答案：D
You know great changes _____________ in our school in the past ten years.
A．have been taken place
B．took place
C．have taken place
D．were taken place
脊前动脉血栓形成最常见于（）
A.延髓
B.脊髓颈胸段
C.脊髓腰段
D.脊髓骶段
E.脊髓圆锥
