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 is the whitest colour in vita shade guide? 
Select and explain. 
A. A1, B. A2, C. B1, D. B2
C: B1
Answer: C: B1 
Explanation: The trend is to arrange shade guides in decreasing order of value (lightest to darkest: B1, A1, B2, D2, A2, C1, C2, D4, A3, D3, B3, A3.5, B4, C3, A4, C4). Matching tooth shades is simplified by the arrangement of tabs by value; this arrangement has been found to be easier and more reliable to use.