The man's actions made it obvious that he had a wicked plan in mind.

Answer: Option B

Obvious : easily perceived or understood; clear, self-evident, or apparent.
False : not according with truth or fact; incorrect.
Obscure : not discovered or known about; uncertain.
Certain : able to be firmly relied on to happen or be the case.
Difficult : needing much effort or skill to accomplish, deal with, or understand.

Antonym of Obvious is Obscure