21．—Can I look at the menu for a few minutes before I decide?

—Of course．______ , sir．

A．Take your time B．It doesn’t matter

C．Enjoy yourself D．Make yourself at home

22．—Why _____ you be talking so loudly while others are studying?

—I am terribly sorry．

A．shall B．must C．will D．may

23．—I find it astonishing that John ______be so rude to me．

—Not astonishing at all．He is always rude to others．

A．should B．must C． might D．ought to

24．—What does the sign over there read?

—No person _______ smoke or carry a lighted cigarette, cigar or pipe in this area．

A．must B．may C．shall D．will