Question

Passengers .....
open the door when the train is moving.
must
mustn't
should
shouldn't
​

Answer 1

Answer:

shouldn't

Explanation:

that is correct grammer because they shouldn't be opening the doors when the train is moving

Answer 2

Answer:

should not

Explanation:

the above sentence is a type of advice for the passengers and we use should/shoud not  to give some sort of advice