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 secondary flare is necessary for class II cast gold inlay preparation for several reasons, but basically the direction of the flare results in: 
Select and explain. 
A. Good aesthetics, B. 60° marginal metal which is burnishable, C. 40° marginal metal which is burnishable, D. 10° marginal metal which is burnishable
C: 40° marginal metal which is burnishable
Answer: C: 40° marginal metal which is burnishable 
Explanation: Secondary flare:
It is a flat plane superimposed peripherally to the primary flare. Advantages are:

Secondary flare ensures cavosurface margins to extend into embrasures (self-cleansing area).
Permits easy burnishing and finishing of the restoration.
Produces more obtuse-angled and stronger cavosurface margin.

In class II cast gold inlay, proximal box should have flares so as to have the metal of 30-40° which is burnishable.