Failure to properly credit the sources of your information is an act of plagiarism. Option B is correct.
Plagiarism is defined as:
the act of stealin and passing off (the ideas or words of another) as one's own
to use (another's production) without crediting the source .
to commit literary theft
to present as new and original an idea or product derived from an existing source
To put it simply, plagiarism is an act of fraud which entails both stealing someone else's work and lying about it afterward.