（） clearances in the main or crank pin bearings will sometimes be indicated by loss of pressure in the lubricating system before any bearing knock is heard.

（） supplies pilot air to control the cylinder air start...

单项选择题（） supplies pilot air to control the cylinder air start valves.

（） may have two emergency source of power, thus requiri...

单项选择题（） may have two emergency source of power, thus requiring two emergency switchboards.

（） usually helps to induce air movement to assist combu...

单项选择题（） usually helps to induce air movement to assist combustion.