The correct option is D the study of fossils
Fossils are any preserved remains or impressions of organisms that lived in a past geological age. These could include the mineralised remains of plants or animals, remnants of bones or even footprints embedded in stratified rocks.
Palaeontology is the branch of science that deals with the study of such fossils.
Study of structure is morphology.
Study of bones is osteology. Though study of fossilised bones would be included under paleontology.