现在完成时的用法?答:如: come→be, come to→be in / at, go out→ be out, leave→be away,begin→be on, stop→ be over, buy→ have, borrow→ keep,open→be open, close→be closed, join→be a member of,die→be dead, catch a cold→have a cold, get to know→know,become a teacher →be a teacher...