Official Solution:

The popular belief that a snake's age can be determined by counting the number of layers of scales on its body is generally true. However, to help regulate its internal temperature, the outermost layers of scales of the Black Mamba snake often peel away when the temperature exceeds 120 degrees Fahrenheit, leaving the snake with fewer layers of scales than it would otherwise have. So only if the temperature in the Black Mamba's environment never exceeds 120 degrees Fahrenheit will its layers be a reliable measure of the snake's age.

Which of the following is an assumption on which the argument is based?

A. The growth of new layers of scales in a snake is not a function of levels of its basal metabolic rate.

B. Only the Black Mamba loses layers of scales because of excessive heat.

C. One day of temperatures above 120 degrees Fahrenheit will cause the Black Mamba snake to lose a layer of scales.

D. The layers of scales of all snakes are of uniform thickness.

E. The number of layers of scales that will be lost when the temperature exceeds 120 degrees Fahrenheit is not predictable.

The argument concludes that one will only be able to determine the age of a Black Mamba by counting its layers of scales if the temperature in the snake's environment never exceeds 120 degrees Fahrenheit. Argument makes this conclusion on the fact that the snake loses layers of scales when the temperature exceeds the level. However, if the number of layers of scales lost by a Black Mamba at high temperatures could be predicted, then it might be possible to determine the age of a snake even if the temperature exceeds 120 degrees. The argument actually assumes that it is not possible to predict the number of layers of scales lost when the temperature exceeds 120 degrees Fahrenheit.

- Choice A : The argument says nothing about basal metabolic rate. This answer choice is out of scope since it would require a number of other assumptions to make it relevant to the argument's conclusion.
- Choice B : Whether other snakes share this feature is irrelevant; the argument focuses only on the Black Mamba.
- Choice C : This choice says that one day of temperatures above 120 degrees = one ring lost. If this is true, then we could actually be able to predict the number of layers of scales lost (if we also know on how many days the temperature exceeded 120 degrees). This damages the author’s argument; therefore, it cannot be an assumption on which the author depends.
- Choice D : The thickness of the layers of scales is irrelevant.
- Choice E : Correct. The argument’s conclusion is that the layers of scales will be a reliable measure only if the temperature never exceeds 120 degrees. This is true only if there is no way to predict how many layers of scales would be lost when the temperature does exceed 120 degrees. (If it were possible to predict this, one might be able to assess the age of a snake using its layers of scales even if the temperature had exceeded 120 degrees.)

Answer: E

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