Select the most appropriate meaning of the given idiom.

To flog a dead horse

The correct answer is "To waste energy on a lost cause"

 Key Points

• 'To flog a dead horse' is an idiom that means to continue putting effort into a lost cause or a situation where it's impossible to make progress.
• It has nothing to do with real horses or beating them. It is a metaphor for wasting time and energy on a futile cause.
• Ex- Even after their team lost the championship, Bob continued arguing about the unfair referee decisions. His friends said he was just flogging a dead horse.
• Therefore, the correct answer is 'Option 2'.