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
The retention of dowel in a pin retained crown is increased by 
Select and explain. 
A. Increased length, smooth surface and increased taper., B. Increased length, serrated surface and increased taper., C. Increased length, smooth surface and parallel sides., D. Increased length, serrated surface and parallel sides.
D: Increased length, serrated surface and parallel sides.
Answer: D: Increased length, serrated surface and parallel sides. 
Explanation: Post should be at least 2/3 the root length, parallel sided and serrated for increased retention in the canal