Choose the alternative which best expresses the meaning of the Idiom/Phrase.
The sportsman worked for donkey's years to win the Olympics.

A long period of time

The answer is a long period of time. The idiom "donkey's years" means a long period of time. It is thought to have originated in the 16th century, when donkeys were used as pack animals. They were known for their endurance and could walk for long distances. So, to say that someone worked for donkey's years means that they worked for a very long time.

The other options do not fit the meaning of the idiom. A short period of time would not be enough time to train for the Olympics. An appropriate period of time would be a reasonable amount of time to train, but it would not be as long as donkey's years. A desired period of time would be the amount of time that the sportsman would have liked to train, but it would not necessarily be a long period of time.