4．
根据对话，补全对话，使对话完整，合乎情景。
A: Hi, Susan. I'm going to the USA as an
exchange student.
B: Great.
A: But I don't know much of the custom and
manners in the USA. ?
B: Sure.
A: ?
B: Well, they think it's important to be on time when
you're
invited to lunch or supper. . Because it is usually planned to
have the meal at the exact hour given in the invitation.
A: ?
B: After the meal is
over. It's not
polite to leave in half an hour , lest（免得）you seem
to have come only for the meal. An evening dinner invitation usually implies
that . The hostess often plans some after-dinner entertainment.
