胃黏膜中分泌盐酸的细胞是
A．主细胞
B．壁细胞
C．黏液细胞
D．G细胞
E．肥大细胞
参考答案：B
青蛙的前后肢的指（趾）间有蹼，有利于游泳．______．
The man we followed suddenly stopped and looked as if ______ whether he was going in the right direction.
A．seeing
B．having seen
C．to see
D．to have seen
