Answer:
This is a run-on sentence.
It's two sentences. The first sentence modifies the second, so, in that sense, is a misplaced modifier, but it is not a phrase within a sentence, it is a different sentence. A run-on sentence occurs when two or more independent clauses (also known as complete sentences) are connected improperly.
The answer is A :)
Hope this helps!
B. Noting which details provide essential support to an author’s main idea is an important study skill.
