$ The animals in which body temperature varies according to the surroundings are called poikilothermal animals.
! Human beings have four chambered heart.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To analyze the assertion and reason provided in the question, we will break it down step by step.

### Step 1: Understand the Assertion
The assertion states that "the animals in which body temperature varies according to the surroundings are called poikilothermal animals."

- **Explanation**: Poikilothermal animals, also known as ectothermic or cold-blooded animals, cannot regulate their body temperature internally. Instead, their body temperature fluctuates with the environmental temperature. Examples include reptiles, amphibians, and most fish.

### Step 2: Understand the Reason
The reason given is "Human beings have a four-chambered heart."

- **Explanation**: Human beings are warm-blooded (endothermic) animals, and they possess a four-chambered heart, which consists of two atria (auricles) and two ventricles. This structure allows for efficient separation of oxygenated and deoxygenated blood, supporting a stable internal body temperature.

### Step 3: Evaluate the Relationship Between Assertion and Reason
Now we need to determine if the reason provided explains the assertion.

- **Analysis**: While both the assertion and the reason are correct statements, the reason does not explain the assertion. The fact that humans have a four-chambered heart is related to their ability to maintain a constant body temperature, but it does not explain why poikilothermal animals have varying body temperatures.

### Conclusion
- **Final Evaluation**: Both the assertion and the reason are true, but the reason does not correctly explain the assertion. Therefore, the correct answer would be that the assertion is true, the reason is true, but the reason is not the correct explanation of the assertion.