You are answering a USMLE-style medical question. Question: An investigator is studying traumatic knee joint injuries in college athletes. Images and tissue samples are collected from 4 athletes with cartilaginous injury and 4 athletes with bone fractures. After 8 weeks, the athletes with bone fractures show almost complete resolution, while the athletes with cartilaginous injuries show only minimal signs of healing. The investigator hypothesizes that this is due to the absence of progenitor cells for matrix regeneration. Transplant of which of the following tissues would most likely promote healing in the group with cartilaginous injury? Options: A) Perichondrium B) Proteoglycans C) Osteoblasts D) Mature chondrocytes Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.