Ramesh and Suresh, two friends went out to a pizza corner. Ramesh bought his favorite pizza, while Suresh was eager to try something new that was suggested by the waiter. So, he purchased a newly arrived dish from the menu. Ramesh happily enjoyed his meal, while Suresh was not happy with his decision. Which of the reinforcement attribute is said to exist in the above situation? Answer Choices: a. Positive reinforcement only b. Negative reinforcement only c. Stimulus generalization d. Both a and b