导致胃酸分泌的内源性物质是（）
A．肾上腺素
B．ACh
C．去甲肾上腺素
D．肽类物质
参考答案：B
无菌药品生产，洁净区门的设计应当便于（）。
Pleasant music is often played _________ classes to make students refreshed and relaxed for a while.
A．after
B．between
C．among
D．over
