内耳道底前面下区是（）。
A.前庭上区
B.前庭下区
C.面神经管区
D.蜗区
E.壶腹区
参考答案：D
He was walking along the river __________ he saw a little boy lying under a tree.[ ]
A. while
B. when
C. as
D. which
低压锅炉酸洗除垢一般都采用（）作为酸洗除垢剂。
