The correct answer is d) deep.
Explanation: In anatomical terms, the skin is considered to be more superficial compared to the bones, which lie deeper within the body. When we describe the relationship between the layers of the body, ‘superficial’ refers to structures closer to the surface, while ‘deep’ describes those that are further inside. Therefore, since the skin is on the outer layer and the bones are underneath, the skin is to the bones as superficial is to deep.