Here's why:
* Simile: A simile is a figure of speech that directly compares two things using words like "like" or "as". In this phrase, "gloomy as the night" directly compares Hector's mood to the darkness of night.
Let's look at why the other options are incorrect:
* Onomatopoeia: This involves words that sound like the noises they describe (e.g., "buzz", "crash"). It's not present here.
* Hyperbole: This is an exaggeration for emphasis. The phrase doesn't exaggerate Hector's gloominess.
* Alliteration: This is the repetition of consonant sounds at the beginning of words (e.g., "Peter Piper picked"). While there is some repetition of the "g" sound, it's not a strong enough example to be considered alliteration.