The answer is: c. classical conditioning
In a classical conditioning, a certain behavior is learned by associating a certain stimulus with either positive or negative response.
For examples, let's say that every time the pets heard the sound electric can opener, the pets would immediately receive their food from their owners.
In the long run, the pets would associate the sound of the electric opener with the positive reward (in the form of food). This make the pets become most likely to experience biological response (such as watering mouth) every time they hear the electric opener.
