Which of the following is not a contract?

• A. A teaches his parrot to speak a proposal and sends it to B. The parrot proposes to B and B gives his acknowledgment to the parrot.
• B. A sits in a public vehicle and takes a ticket
• C. A stands at a weighing machine at a railway station and puts a coin in it
• D. A gives an advertisement that whoever brings his lost dog will get a reward and brings B to him