(D) all of the above
Mutated plasmablasts in the bone marrow undergo replication and expand the plasma cell mass. Normal bone marrow is gradually replaced with malignant plasma cells leading to pancytopenia (low level of all blood cell types). Malignant plasma cells usually increase the production of immunoglobulins. The production of light chains and heavy chains are imbalanced resulting in additional release of light chain and free heavy chains. Any antibodies produced by the malignant cells are referred to as monoclonal gammopathy. Osteoclasts (bone cells) are active in using calcium in the blood to form new bone. Multiple myeloma interrupts the balance by the secretion of interleukin-6 (IL-6) and osteoclast-activating factor (OAF). OAF stimulates osteoclasts to increase bone resorption and release of calcium, which leads to lesions of the bone.
Harr, R. ;Clinical Laboratory Science Review third edition, pg28
(B) 1,25-dihydroxycholecalciferol (1,25-[OH]2-D3)
When Vitamin D is obtained it is converted in the liver to 25-hydroxycholecalciferol (25-OH-D3) which is still an inactive form of Vitamin D. In the kidney, 25-OH-D3 is hydroxylated to form 1,25-dihydroxycholecalciferol (1,25-[OH]2-D3, the biologically active form of Vitamin D. This active form of Vitamin D increases Calcium absorption in the intestine and enhances the effect of PTH on bone resorption. Calcitonin is secreted by the thyroid gland when the concentration of calcium in blood increases.
Bishop, M.; Clinical Chemistry Techniques, Principles, Correlations sixth edition, pg 373