离心泵的主要优点？
参考答案：
离心泵的主要具有转速高、体积小、重量轻、效率高、效率大、结构简单，性能平稳，容易操作和维修方便等特点。
因式分解:x2-9=（ ）。
So desperate ________ that no one could help another, each ________ to save himself and his animals.[ ]
A．was the situation; was trying
B．the situation was; trying
C．the situation was; was trying
D．was the situation; trying
