Answer:
A primary Circular reaction.
Step-by-step explanation:
Bejamin is going thru a primary circular reaction. Based on his age and as the action he is performing is common in all of the children, sucking his thumb.
The primary circular reaction is a stage of cognitive development that happens between the 1st and the 4th month. The infant develops an accident action and then intentionally repeats it as he finds it pleasurable while learning to coordinate his movements in order to achieve the goal which is sticking his thumb in his mouth to find pleasure again.