Select the most appropriate meaning of the underlined idiom in the given sentence.

The police was able to find the guilty but the big fish escaped.

main leaders

The most appropriate meaning of the underlined idiom in the given sentence is main leaders.

The idiom "big fish" refers to the main leaders or the most important people in a group or organization. It is often used in a negative way to suggest that these people are able to escape punishment or responsibility because of their power or influence.

In the given sentence, the police were able to find the guilty people involved in a crime, but the main leaders who were responsible for the crime were able to escape. This is a common occurrence, as powerful people often have the resources and connections to avoid being caught or punished.

The other options are not as appropriate. Plump men, large-sized ones, and tall people are not necessarily the main leaders in a group or organization.