For a song 便宜的，以很低的价格
You can always buy some antiques for a song at this market.
Common-law marriage 同居
They have been in a common-law marriage for six years and still don't want to get married.
My common-law husband is a sweet person and we enjoy feeling in love with each other every day.
As clean as a whistle 非常洁净，清白，空的，灵敏的
The police tried to find evidence related to his criminal behaviour but he was as clean as a whistle.
Mary rides on the horse and jumps over the barrier as clean as a whistle.
The feed pipe is as clean as whistle, so I'm afraid, if the oil is not getting through to the burner, the valve must be faulty.
Carry coals to Newcastle 多此一举
You are carrying coals to
Telling the doctor how to cure a cold is carrying coals to
Giving her flowers is taking coals to
