Training a dog to respond to the word "good" as a conditioned reinforcer is accomplished by saying "good"
a. at the same time as presenting a piece of food.
b. immediately after presenting a piece of food.
c. just before presenting a piece of food.
d. repeatedly while using a clicker.

The correct option is C.
Primary reinforcer refers to the basic needs of an animal, such as food, water, shelter, etc. Secondary reinforcer, which is also called condition reinforcer refers to the condition in which a stimulus reinforces a behavior after it had been associated with a primary reinforcer.
In the question given above, the primary reiforcer is food.