钠水玻璃的硬化方法有几种？
参考答案：物理硬化----自然干燥或加热和吹压缩空气；化学硬化----
插管法和盖罩法等两种
With a lot of difficult problems , the manager felt like a cat on hot bricks.
A．to settle
B．settling
C．settled
D．being settled
齿轮泵的主要工作特点是什麽？
