seem to be doing sth表示不定式的动作和主句中seem是同一个时态，比如，He seems to be doing his homework. 他好像正在做作业；seem to do 表示不定式的动作发生在主句动词seem之后，比如It seems to rain. 好像要下雨了。 rain的动作，是发生在seem之后的；seem to have done sth表示不定式的动作发生在主句动词seem之前，比如 she seems to have finished her homework. 她好像做完了她的家庭作业。finish的动作发生在seem之前
