This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Osteoblasts produce - 
Select and explain. 
A. Collagen, B. Calcium, C. Pyrophosphate, D. Monosodium urate
A: Collagen
Answer: A: Collagen 
Explanation: Osteoblast-Derived Proteins
Type 1 collagen
Cell adhesion proteins 
     osteopontin, fibronectin, thrombospondin
Calcium-binding proteins
     Osteonectin, bone sialoprotein
Proteins involved in mineralization
    Osteocalcin 
Enzymes
    Collagenase, alkaline phosphatase
Growth factors
   IGF-1, TGF-β, PDGF
Cytokines
   Prostaglandins, IL-1, IL-6, RANKL
Proteins Concentrated from Serum
β2-microglobulin
Albumin