这里的would you只是必须的客气话,回答就说 yes,why not./Yes,please.或Yes,good idea.否定的话,No,thanks.但是,请看下面的句子：if it was you,would you do that?if she wasn't my girlfriend,would you ask her out?这样的句子,用Yes,I would和No,I wouldn't就是合适的,Would you like sth/to do/doing sth用Yes,I would或No,I wouldn't就有点别扭了,因为这里的would只是必须的客气话