In grammar, two or more elements can be compared by using comparative and superlative forms in the case of adjective that are words that describe nouns the comparative is formed by adding "-er" in case of short adjectives or "more" in case of longer adjectives. However, in the case of adverbs that describe verbs rather than nouns and in most cases end in "-ly" the comparative form is created by using the word "more". This implies in the case of the sentence "Dogs and coyotes are ________ related than cats and fish" the words that complete this sentence are "more closely" as in this case the comparison is established in relation to the verb "are related" and therefore the adverb "closely" need to be preceded by the word "more" to establish a comparison, also this is the only answer that is grammatical correct as others do not follow the rules about comparatives formation.
