Final answer:
The adjectives 'biggest' and 'fiercest' in the sentence modify the noun 'fish,' and emphasize the characteristics of sharks as sizable and aggressive predators.
Step-by-step explanation:
In the sentence "Some of the biggest and fiercest fish on Earth are sharks," we are tasked with identifying adjectives and the words they modify. The adjectives in this sentence are 'biggest' and 'fiercest.' The word 'biggest' is a superlative adjective, and 'fiercest' is a strong descriptive adjective. Both adjectives modify the noun 'fish,' telling us more about the size and nature of the fish being described. The sentence emphasizes the characteristics of sharks, particularly highlighting their size and predatory nature, which is consistent with their biological classification as powerful predators among cartilaginous fish.