防汛保证水位是指保证江河、湖泊、水库在汛期安全运行的（）水位。
A.上限
B.下限
C.日常
D.一般
参考答案：A
My teacher often sits between Jim and______. [ ]
A. mine
B. my
C.me
D. I
胃穿透性溃疡系指溃疡侵及（）
A.黏膜层
B.黏膜下层
C.肌层
D.浆膜层
E.黏膜和黏膜下层
