In the as-quenched state, martensite is very hard and so brittle that a heat treatment known as_________must be accomplished sequently. A: normalizing B: annealing C: tempering D: austempering

Themedicine（）cool,cleananddry. A: must  keep B: must  be  kept C: must  be  keep D: must  be  in

The flowers ( ) every day. A: must be water B: must be watered C: must watered D: must water

Such films _____ by children like you. A: must be not seen B: must not be see C: must not seen D: must not be seen

These books ______ good care of. A: must taken B: must take C: must to take D: must be taken

The medicine （） cool, clean and dry. A: must keep B: must be kept C: must be keep D: must be i

The flowers （） often. A: must be water B: must be watered C: must watered

Old people () carefully. A: must be listened B: must be listened to C: must listen to

He looks tired. He ______ a sleepless night. A: must have been B: must have had C: must be D: must have

The construction of the laboratory ________ by the end of July. A: must be completing B: must complete C: must have complete D: must have been completed