Which sentence from The Phantom Tollbooth is the best example of using an idiom for humorous effect?

c."It's bad enough wasting time without killing it."

Explanation:

An idiom is a phrase whose meaning may not be deducible from the literal words used. 'Killing time' is an idiom which means wasting time. the phrase was used by the watchdog in the book the phantom tollbooth. An idiom is used for humorous effect when it evokes laughter in the audience.

The dog's purpose was to make sure that people do not waste time. So when he was told that he was killing time he became annoyed and made the statement, "It's bad enough wasting time without killing it."