Final answer:
The word that best matches 'cavernous' is 'cave-like' because both refer to large hollow spaces or cavities.
Step-by-step explanation:
The word or phrase that best matches the word 'cavernous' is 'cave-like'. Cavernous means having large hollow spaces or cavities, just like a cave. Therefore, when looking into the whale's cavernous mouth, it would be similar to looking into a cave with darkness.
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