When Thor, Glen’s dog, brought a pinecone instead of a ball, he is displaying a concept in operant conditioning that often occurs to the subject, which is called (C) stimulus generalization.
Thor expects to receive the same response by bringing a pinecone instead of a ball because he perceives, perhaps, the perceives both stimuli as the same. It could be due to similarity of size, color, or location between the pinecone and the ball which caused Thor to do this.