Final answer:
Kangaroo rats have adapted to the arid desert environment primarily through their efficient kidneys that conserve water, which is a critical adaptation for desert survival, making Option 1 the correct answer.
Step-by-step explanation:
Kangaroo rats are remarkable desert-dwelling organisms that have developed several adaptations to survive in their arid habitat. One crucial adaptation is their efficient water conservation, which is vital in a hot, dry climate. Unlike many animals, kangaroo rats have highly efficient kidneys that produce highly concentrated urine, drastically reducing water loss from their bodies.
This ability to store water effectively, similar to how the Gila monster stores water in its fat tail, is arguably their most important adaptation. Without the need to drink water frequently, they can survive the harsh desert environment. Large body size would not be advantageous in the desert, as it could increase water requirements. Thick fur, while providing insulation, is not specifically an adaptation for conserving water. High sensitivity to light is also not directly related to water conservation, although it may aid in nocturnal behavior to avoid daytime heat.
Therefore, the answer is Option 1: Ability to store water efficiently. This adaptation, along with behavioral changes such as seeking cooler areas during the day and capturing heat at night, enables kangaroo rats to thrive in the desert climate.