Why do historians have to include a citation when paraphrasing an idea from another source

I believe it may be C. or B?
Explanation:
Why C?
When you include a citation it's giving the other person credit who originally had the idea, so people won't think or assume you stole the idea or thought of the idea yourself.
Why B?
Corroborated means: to make more certain; confirm or back up your information.
Hope this made sense and helped a little?