The correct answer is A. This is the case of using comma before a coordinating conjunction <em>and</em> because it links two independent clauses. We can observe that there two parts of this full sentence and each part is independent from each other. Both of them have their own subject and verb. Therefore, we are using a comma before <em>and</em>.
Among the given sentences above, the sentence that is correctly written is option A. In June 1776, Thomas Jefferson <span>wrote the first draft of the Declaration of Independence, and it was formally adopted by Congress on July 4 of that year. This sentence is correctly written because as you noticed it, it is using the conjunction "and" and a comma before it, in order to avoid a run-on sentence. </span>
