Which type of word is used to connect two sentences together?

The correct choice is a conjunction. A conjunction is specifically a part of speech that serves the purpose of linking words, phrases, or clauses together, allowing for the formation of more complex sentences. This function is crucial in enhancing the fluidity and coherence of the text, as it creates connections between different ideas, enabling a smoother transition.

For example, common conjunctions like "and," "but," and "or" are frequently used to connect two independent sentences, creating compound sentences that convey more intricate relationships between thought processes. This addition of nuance and flow exemplifies the essential role of conjunctions in writing and speech.

Other types of words like prepositions, adverbs, and pronouns have different functions that do not pertain to connecting whole sentences. Prepositions indicate relationships between nouns and other words, adverbs modify verbs, adjectives, or other adverbs, and pronouns replace nouns to avoid repetition. Each serves its distinct purpose in language, but it is the conjunction that specifically fulfills the need to connect two sentences together.