Which of the following statements is tree about his friend a. Writing exhausts his friend. b. His friend collects a lot of things to write. c. His friend always has enough material to write on. d. His friend is doing research to write a paper.

在流体高温，腐蚀性强，含有固体颗粒量大的场合，常用的机械密封冲洗方式是（）。

A.自冲洗

B.反冲洗

C.贯穿冲洗

D.外冲洗