The popular notion that a tree's age can be determined by counting number of internal rings in its trunk is generally true. Howeevr, to help regulate the internal temperature of the tree, the outermost layers of wood of the Brazilian ash often $\stackrel{peel}{\to }$ 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 $\stackrel{elaveing}{\to }$ the tree with fewer rings than it would otherwise have. So only if the reliable measure of the tree's age. Which of the following is an assumption on whish the argument above depends?