Respuesta :
The Adverb clause is, Where old coral reefs rose above the sea.
The adverb clause in the sentence is "where old coral reefs rose above the sea". Adverb clauses are subordinate clauses that modify other adverbs, adjectives or verbs in a sentence.
In this case, the adverb clause is modifying the adverb phrase "North Pacific Ocean".
Adverb clauses are introduced by subordinating conjunctions. In this case, the subordinating conjunction is "where".
