What is Article 13 about? What does it say?  Article 13 is about____ . The article says, “If you_____ , you must______.”

All equipment in an aircraft must______. A: be tested to destruction B: not be too light in weight C: work especially well at high temperatures D: work perfectly within a wide range of temperatures

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