滤层结垢降低滤层（），使滤后的水质不合格。
A、过滤面积
B、有效过滤面积
C、厚度
D、质量
参考答案：B
Since everyone would like to find an apartment near the university, there are very few ____ apartments in the area.
A．free
B．vacant
C．empty
D．reserved
下列不属于局部麻醉的是（）。
A.神经丛（节）阻滞
B.咽腔内黏膜麻醉
C.硬脊膜外阻滞
D.神经阻滞
E.区域阻滞
