Think of stimulating phrases to which the phrases below are the replies
I am afraid not
No,you(he,she,they)mustn't

Will you join us today at lunch? - I am afraid notMust I tell them the whole story? - No, you mustn'tMust she ring when she arrives? - No, she mustn'tMust he bring his bag for checking? - No, he mustn'tMust they take us with them? - No, they mustn't