After Training One of His Dogs to Salivate in Response

Multiple Choice

After training one of his dogs to salivate in response to a tone,Pavlov continued to present the tone periodically without the food.What did the dog do

A)  It kept responding at the same intensity, despite extended exposure to the tone alone. 
B)  It stopped responding immediately. 
C)  It initially responded to the tone at an even greater intensity than before. 
D)  It gradually stopped responding to the tone.