Critical Reasoning

The popular notion that a tree's age can be determined by counting the number of internal rings in its trunk is generally true. However, to help regulate the internal temperature of the tree, the outermost layers of wood of the Brazilian ash often peel away when the temperature exceeds 95 degrees Fahrenheit, leaving the tree with fewer rings than it would otherwise have. So only if the temperature in the Brazilian ash's environment never exceeds 95 degrees Fahrenheit will its rings be a reliable measure of the tree's age.

Which of the following is an assumption on which the argument above depends?
A) The growth of new rings in a tree is not a function of levels of precipitation.
B) Only the Brazilian ash loses rings because of excessive heat.
C) Only one day of temperatures above 95 degrees Fahrenheit is needed to cause the Brazilian ash to lose a ring.
D) The internal rings of all trees are of uniform thickness.
E) The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is not predictable.

OA E
Why not C, OE says it is irrelevant. I'd like to know why?
Pls explain your answers
source : MGMAT

IMO E
A: Irrelevant
B: Irrelevant
C: The stimulus tells us that when the temperature exceeds 95 degrees Fahrenheit, the outermost layers peel away. It doesn't tell us about duration. This can happen when the temperature exceeds 95 degrees for less than a day or more than a day.
D: Irrelevant

Only E gives us the right assumption that if we can't predict the number of rings lost when temperature exceeds 95 degrees Fahrenheit, we can't determine the tree's age.

Try negating this assumption. Let us say that we can predict the number of rings lost due to temperature exceeding 95 degrees Fahrenheit. In that case we know the total number of rings for the tree (rings present in the tree and the number of rings that was lost due to temp exceeding 95). Hence we can predict the age.

IMO - E, @SanjeevK has given a perfect explanation.

Looking at it now, E makes sense