Answer:
b. did not know of the reward when he returned the dog.
Explanation:
Laredo advertises for getting his dog back. This does not infer that the dog will only be returned when the reward will be paid.
Miguel did not know about the reward, so the reward in this case is not mandatory to be paid, but if Laredo initiates the reward himself, that can be accepted.
This is a clear demonstration of being kind and get what you know.
So if you do not know the facts, you are on fault.