Pavlov Was Able to Train Dogs to Salivate at the Sound

Pavlov was able to train dogs to salivate at the sound of a bell by pairing the dogs' natural response to salivate at the sight of food with a bell. When the bell was rung each time food was presented, the dog learned that the bell signaled food was coming and began salivating. After enough repetition, the dog began to salivate with just the sound of the bell. What is this called?

A) Classical conditioning
B) Operant conditioning
C) Reinforcement training
D) Punishment training