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: Dental
Residual ridge resorption is: 
Select and explain. 
A. Directly proportional to the anatomic factor., B. Indirectly proportional to the force., C. Directly proportional to the damping effect., D. Directly proportional to the bone-forming factors.
A: Directly proportional to the anatomic factor.
Answer: A: Directly proportional to the anatomic factor. 
Explanation: None