Final answer:
The linking verb is 'are' and the predicate noun is 'the fastest runners on our cross-country team.'
Step-by-step explanation:
The linking verb in the sentence is 'are.' It connects the subject 'Hugo and Isaiah' to the predicate noun or predicate adjective. In this case, the predicate noun is 'the fastest runners on our cross-country team.'
Learn more about Linking verbs and predicate nouns/adjectives