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
Which of these is not a basic principle of radiation protection ? 
Select and explain. 
A. Justification, B. Collimation, C. Limitation, D. Optimization
B: Collimation
Answer: B: Collimation 
Explanation: In addition to the three basic principles of radiation protection (justification, limitation, and optimization), one  can apply the following additional techniques to reduce the radiation burden to the patient:

Collimation of the x-ray beam.
Correct focus-to-skin distance.
Lead apron with thyroid collar.
More radiation-sensitive image receptors.