Which of the following provides evidence that infants possess core knowledge about solid objects?

(a) Infants can use a reaching tool to retrieve a solid object that is stuck behind a barrier
(b) Infants preferentially look at events where solid objects appear to pass through each other
(c) Infants spontaneously search for a solid object that has been removed out of their sight
(d) Infants are able to grasp solid objects and bring them to their mouth to stuck on.