What do osteoblasts predominantly add to bones besides collagen?

Osteoblasts are specialized cells responsible for bone formation. While collagen is a significant component that provides structural framework and tensile strength to the bone, osteoblasts also play a crucial role in the deposition of various minerals into the bone matrix, primarily hydroxyapatite, which is composed of calcium and phosphorus.

The choice of "D. Minerals" encompasses a broad range of inorganic substances that osteoblasts contribute to, including calcium, phosphorus, and other trace elements necessary for bone strength and health. This is why the correct answer is "D. Minerals." By focusing on minerals in general, it captures the overall function of osteoblasts in promoting bone mineralization, which is essential for maintaining the rigidity and strength of bones.

Collagen forms the organic part of the bone matrix, while the minerals provide the inorganic part that ultimately allows bones to support weight and withstand stress. Therefore, the answer recognizes the comprehensive role of osteoblasts in bone synthesis and mineralization, affirming their critical function as bone builders beyond just collagen production.