[A]: The first life originated was chemoheterotrophic.
[R]: The first life originated in sea water.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**: The assertion states that the first life forms were chemoheterotrophic. Chemoheterotrophs are organisms that obtain their energy and carbon from organic compounds. This implies that the first life forms relied on pre-existing organic molecules for their nutrition.

2. **Understanding the Reason (R)**: The reason states that the first life originated in seawater. This suggests that the environment of seawater played a crucial role in the emergence of life.

3. **Analyzing the Relationship**: To determine if R is a correct explanation of A, we need to consider the conditions in seawater. Seawater is rich in organic molecules, which would provide the necessary nutrients for chemoheterotrophic organisms. Therefore, the assertion that the first life forms were chemoheterotrophic is supported by the reason that they originated in an environment abundant in organic materials.

4. **Conclusion**: Both the assertion (A) and the reason (R) are true. Furthermore, R correctly explains A because the presence of organic molecules in seawater would have facilitated the existence of chemoheterotrophic life forms.

5. **Final Answer**: The correct option is A: Both A and R are true, and R is the correct explanation of A.