$\frac{I_{max}}{I_{min}} = \left( \frac{a_1 + a_2}{a_1 - a_2} \right)^2 = 16 \implies \frac{a_1 + a_2}{a_1 - a_2} = 4$.

$a_1 + a_2 = 4a_1 - 4a_2 \implies 5a_2 = 3a_1 \implies \frac{a_1}{a_2} = \frac{5}{3}$.

Intensity ratio $\frac{I_1}{I_2} = \left( \frac{a_1}{a_2} \right)^2 = \frac{25}{9}$.

This three-blank question rewards careful reading of each clause.

Blank (i): The sentence argues that even someone not paying close attention would notice the historical difference in fish abundance. This is a rhetorical device lowering the bar — even the most casual (inattentive, uninterested) observer would see it. Using “prescient” (having foresight) or “clearheaded” would raise the bar rather than lower it, weakening the rhetorical effect.

Blank (ii): The passage envisions the past ocean as healthy and full. So those formerly abundant marine mammal species would appear plentiful (abundant, numerous). “Threatened” implies danger, contradicting the image of a healthy past ocean, and “unfamiliar” does not fit the logic.

Blank (iii): Without the magic glasses, we cannot easily perceive or recognize the difference between past and present oceans. Discern means to perceive or recognize clearly — perfect. “Ignore” and “dismiss” imply active rejection, not the passive difficulty of perception described.

Correct Answers: Blank (i) = A (casual), Blank (ii) = E (plentiful), Blank (iii) = H (discern).