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
Two or more parallel vertical surfaces of abutment teeth shaped to direct the prosthesis during placement and removal, are known as: 
Select and explain. 
A. Orientation plane, B. Parallel block out, C. Survey lines, D. Guiding planes
D: Guiding planes
Answer: D: Guiding planes 
Explanation: None