理换离心泵密封填料时，在轴套上把密封填料填好，并量取双圈长度。
参考答案：错
I soon found that the work I was doing had already been done by someone else－ , I was wasting my time.
A．what’s worse
B．all in all
C．all the best
D．in other words
我国十六世纪以前对药学贡献最大的著作（）
A、本草图经
B、本草纲目拾遗
C、植物名实图考
D、证类本草E本草纲目
