Joe Sees a Dog Wandering Around His Yard

Joe sees a dog wandering around his yard.He lets the dog in.Later he learns that the dog belongs to Mary,a woman who lives a kilometre away.Joe returns the dog to her the next day.A few days later as Joe is riding his bike,he sees an old advert in which Mary offers to pay $100 to any person who will find and return her dog.Joe realizes that he should have claimed the reward at the time that he returned the dog to Mary,and he decides to go to Mary's place.Which of the following is true?

A) Joe will be entitled to the reward because he found the dog and returned it.
B) Joe will not be entitled to the reward because Mary made no offer.
C) Joe will not be entitled to the reward because he did not see the offer of the reward until he had returned the dog and so he did not act in response to the offer of Mary.
D) Mary's advert is an invitation to do business and cannot give rise to a contract.
E) Joe will be entitled to the reward because Mary made an offer and his act of finding and returning the dog is an acceptance.