This is important to keep the essay on the main idea. Sentence structures could be simple (one independent clause), compound (two independent clause with coordinating conjunction), complex (a subordinate & independent clause) and compound-complex sentences (subordinate & two independent clause). These include clauses, conjunctions, coherence and balance and even to the number of words you use in your subject and predicate. You must also see to it that when you do parallelism, your sentences still makes sense. The answer is B. By joining two simple sentences with a comma and a coordinate conjunction