Answer: overall i think A is your answer
While a period ends a sentence, a comma indicates a smaller break. Some writers think of a comma as a soft pause—a punctuation mark that separates words, clauses, or ideas within a sentence. Here's a tip: Commas can be tricky, but they don't have to trip you up.
Explanation: choose the one that does not make sense like for example, B.
a comma cannot separate two independent clauses unless it is followed by a coordinating conjunction
A. Use commas to separate words and word groups in a simple series of three or more items. Example: My estate goes to my husband, son, daughter-in-law, and nephew. Note: When the last comma in a series comes before and or or (after daughter-in-law in the above example), it is known as the Oxford comma.
C. Use a comma (or a pair of commas) to set off elements that are nonessential (also called nonrestrictive). A phrase or clause is nonessential if it can be removed without changing the main idea of the sentence; a nonessential element just adds a relatively unimportant detail.
D. Use a comma after transition words and phrases that begin a sentence: however, therefore, on the other hand, for example, etc. Use a pair of commas in the middle of a sentence to set off transition words and phrases as well as clauses that are not essential to the meaning of the sentence.
