Irinia's Dog Loves to Go for Walks,and She Always Puts

Irinia's dog loves to go for walks,and she always puts a leash on him when they go out.At first,the dog wagged his tail only when they got outside;eventually,he began to wag his tail when she picked up the leash.Irinia recently locked herself out of her place,so she has begun picking up her keys and putting them in her pocket before she takes down the leash.Now the dog begins to wag his tail when she picks up her keys.What kind of learning has happened?

A) Operant conditioning
B) Discriminatory
C) Higher-order conditioning
D) Persistence