Final answer:
Conjunctions are the part of speech used to connect words and groups of words, such as phrases and clauses, and are essential for smooth and coherent writing.
Step-by-step explanation:
Of the eight parts of speech, conjunctions are used to connect words and groups of words. This includes connecting phrases and clauses within sentences to show relationships between ideas and ensure that our writing flows smoothly. Conjunctions are essential for creating clear and coherent writing that readers can follow easily. While there are many parts of speech, including nouns, verbs, adverbs, and adjectives, which are used frequently, it is the conjunction that plays the pivotal role in tying these words and phrases together.