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