The correct answer is option 'C', which states that a thick layer of fat helps the whale to protect itself in cold temperatures. Let's understand why this is the correct answer.

Thick Layer of Fat:
One of the key adaptations of whales to survive in cold temperatures is their thick layer of fat, known as blubber. This blubber acts as an insulating layer that helps to keep the whale warm in cold water. Here's why the thick layer of fat is crucial for their survival:

1. Insulation: The blubber acts as a natural insulation that prevents heat loss from the whale's body. It helps to maintain a stable body temperature even in extremely cold water. The fat layer is an excellent insulator because it is not easily conductive, meaning it does not readily transfer heat. This insulation is essential as it helps the whale to conserve its body heat and stay warm.

2. Energy Reserves: The thick layer of fat also serves as an energy reserve for the whale. Whales migrate long distances to find food or reach breeding grounds. During these journeys, they may not find enough food sources. The stored fat can be used as an energy source during periods of fasting or limited food availability.

3. Buoyancy: The blubber not only keeps whales warm but also provides buoyancy in water. It helps the whale to stay afloat and maintain its position in the water column. This is especially important for deep-diving species that need to control their buoyancy during dives.

4. Protection: Apart from insulation and energy reserves, the thick layer of fat also provides a certain level of protection to the whale's internal organs. It acts as a cushion, absorbing shocks and protecting vital organs from external impacts.

In summary, the thick layer of fat, or blubber, is a vital adaptation of whales to survive in cold temperatures. It provides insulation, energy reserves, buoyancy, and protection to the whale's body, allowing it to thrive in chilly ocean environments.