The correct answer is D. Comma splice
Explanation:
An independent clause is a clause (grammatical unit) that expresses a complete thought and therefore does not need other clause or grammatical elements to stand and be independent. Additionally, an independent clause can be combined with other independent clauses to express more than one idea or with non-independent clauses to express more than one idea or to make one idea more complex.
In the case of combining two independent clauses the most correct way is to use a semicolon or a comma and a coordinating conjunction; using only a comma will lead to a "comma splice" which is linking two independent clauses only with a comma but not an appropriate conjunction, this is usually considered as a writing mistake, but in some cases it is accepted in informal situations. Thus, the use of a comma to join two independent clauses is called a comma splice as two clauses are being linked by a comma but it not grammatically correct and these are not linked appropriately.
