Correct choice is (d) Bone Marrow
To explain I would say: Bone marrow is a soft tissue as compared to the encasing bone structure. Also, it had water whose Hydrogen is used by the MRI to form an image. The other parts of the bone do contain hydrogen but the hydrogen is placed in a crystal structure, making it difficult to move or be magnetized. Thus, it is difficult to image any other parts of the bone with MRI except for the bone marrow.