We must purify the

We must purify the oil purifier,oil recycling 是什么?We need oil purifier to purify our lubricant oil.This oil recycling machine must be good quality. we must call the we must o______ the rules purify my we must keep the ( )on the road we must keep the( ) on the road We must shoot the arrow at the we must ()when the light is yellowAgoBcrossCwait we must have missed you along the We must be careful_____(cross) the road. We must be quiet in the library. Must we 【start】 the work at once 改错 We must keep the classroom cleanly. We must ___(keep) the classroom clean. We must find sb___(do) the job. We must be l------- to the school We must keep the window______(open).