These acid residues must be prevented from entering the crankcase, otherwise the lube oil would be .

He won the scholarship. He ______ hard these terms.A．should have workedB．must have workedC

答案解析

The soda－acid portable extinguishers must be discharged and refilled _____.A.every six mon

答案解析

You can exercise your imagination, but these exercises must be done in accordance with the

答案解析

－－－ Was that the headmaster who walked by？ －－－ _______.A、It must be thatB、It must be him

答案解析

When we are in a social gathering, we must be aware of the rules and procedures that govern the way things are going to proceed. These rules and procedures are technically called（).

答案解析

New drugs or devices must be tested before being

答案解析

Some people are accustomed to thinking that facts must either be believed or they must be

答案解析