I think the answer is c. Sentence 3
Sorry if wrong
<span>A central or a main idea is an idea around which your entire paper or essay or paragraph or whatever it is you're writing, revolves. You have a central idea that you're trying to convey and everything you write or say somehow relates to that idea and proves a point that you're trying to make.</span>
Answer:
But indicates a cause /effect relationship.
The answer here is probably B, but you didn’t provide the text so I can’t be sure.
