The crankcase cover should never be allowed to open for investigation when （）

[单选题]The crank-room cover should not be opened until at least （） minutes after the engine stops.A . oneB . fifteenC . sixtyD . ninety

[单选题]：Keys should never be hidden around the house since thieves（ ）know where to find them．A．virtuallyB．unavoidablyC．reliablyD．invariably

[单选题]Teenagers should never give any strangers ______.A． their mobile phone numbersB． their family addressC． their personal informationD． their parents’ names

[判断题]War risks should be added to the main insurance cover.（ ）A.对B.错

[判断题]War risks should be added to the main insurance cover.（ ）A.对B.错

[问答题]Study the following graphs carefully and write an essay in 160-200 words. Y

[单选题]C．rankcase explosions in propulsion diesel engines result fromA．the splashing of lubrication oil by the crankshaftB．the dilution of crankcase oil with particles of combustionC．broken fuel lines spraying oil on the crankcaseD．the ignition of unburned

[单选题]C．rankcase explosions in propulsion diesel engines result from ____.A．the splashing of lubrication oil by the crankshaftB．the dilution of crankcase oil with particles of combustionC．broken fuel lines spraying oil on the crankcaseD．the ignition of unb

[单选题]The crankcase can not be opened （）the parts have been cooled down.A . ifB . asC . unlessD . whe

[单选题]Regarding a Diesel engine crankcase, the general arrangement and installation should preclude the possibility of （）A . free entry of air to the crankcaseB . water entering the crankcase while engine wash-downs are being performedC . excessive oil lea