Answer:
C) Coastal regions, where climate is moderated by warmer ocean waters, have abundant flora and fauna.
Explanation:
An adjective clause is a type of dependent clause whose function is to modify or describe nouns. Very often, an adjective clause may begin with a relative pronoun, namely, who, whom, whose, that, or which, or a relative adverb, namely, when, where, or why.
The sentence from option C is the only one that combines the two sentences using an adjective clause. In this sentence, “where climate is moderated by warmer ocean waters” is the adjective clause: it describes or gives further detail to the noun <em>coastal regions</em> and it begins with the relative adverb <em>where</em>.