This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Special Senses: Vision and its Elements, Subject name: Physiology
All the following are primary colours except 
Select and explain. 
A. Blue, B. Green, C. Red, D. Yellow
D: Yellow
Answer: D: Yellow 
Explanation: (D) Yellow > Blue, green and red are the primary colours but the cones with their maximal sensitivity in the yellow portion of sensitive enough in red portion to respond to red light at a lower threshold than green