Which of the following would indicate that a baby has the conceptual category of "motor vehicles"?

a) The infant habituates after repeatedly being shown pictures of cars.
b) After repeatedly being shown pictures of cars, the infant recovers to a picture of a truck.
c) After repeatedly being shown pictures of cars, trucks, and vans, the infant does not recover to a picture of a house.
d) The infant prefers pictures of cars that they've ridden in before.
e) After repeatedly being shown pictures of cars, trucks, and vans, the infant recovers to a picture of a house.