Select the most appropriate meaning of the given idiom.

A drug in the market

A unsaleable thing due to lack of demand

The most appropriate meaning of the idiom "a drug in the market" is a unsaleable thing due to lack of demand. This idiom is often used to describe a product or service that is no longer in demand and is therefore difficult to sell. For example, you might say "The new product was a drug in the market, and the company had to discontinue it."

The other possible meanings of the idiom are not as common. "A selfish friend" is someone who only cares about themselves and their own needs. "Tit for tat" means to do something to someone in return for something they have done to you. "No longer in use" means something that is no longer used or needed.