1.Pigs might fly.2.When pigs fly.3.Drive one's pigs to markets.4Make a pig of oneself.

1、奇迹可能会发生.2、不可能的事“除非天上掉馅饼”.eg：,"Do you think Mary will quit her job now that she's pregnant?"另一个人就回答,"Yeah,when pigs fly!There is no way she is giving up her career!"当...