囊式封堵器适用的介质范围是（） ["原油、成品油、水","原油、成品油、水、天然气、煤气等","不适用于可燃性气体","原油、成品油"]
Which is the correct command to back up the database， back up the archived redo logs， and then remove the backed-up archived redo logs？（） [" backup database"," backup database and archivelogs"," backup database plus archivelogs"," backup database plus archivelog delete input"," backup database and archivelog delete input"]
下列关于梁中钢筋保护层厚度的说法，正确的是（）。 ["主筋表面至梁表面的距离","主筋形心至梁表面的距离","箍筋表面至梁表面的距离","箍筋形心至梁表面的距离"]
注入催化裂化反应器安全阀防焦蒸汽、再生器的稀相注汽、减压炉和焦化加热的炉管注汽、催化裂化提升管预提升蒸汽的目的是（）。 ["加热用蒸汽","用于催化裂化反应器进料雾化","用于吹扫、事故、消防用汽","降低油汽分压、增加流速、缩短停留时间"]
An administrator received a call from a user whose PC crashed while using vi to edit a file. The user wants the edited file back. Where should the administrator look for the file（） ["\/tmp","\/var\/preserve","\/var\/tmp\/$USER","$HOME\/.vi"]
生态系统中的信息流
