[A]: The earliest living organisms were truc-turally simple.
[R]: The earliest living organisms were more complex than present one.

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

To analyze the given statements regarding the earliest living organisms, we will break down the assertion and reason, and then evaluate their truthfulness.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "The earliest living organisms were structurally simple."
- This statement refers to the nature of the first life forms on Earth, which were primarily prokaryotic cells (like bacteria). Prokaryotes are characterized by their simple structure, lacking a nucleus and membrane-bound organelles.

2. **Understanding the Reason (R)**:
- The reason states that "The earliest living organisms were more complex than present ones."
- This statement suggests that the first organisms were more advanced in structure compared to current organisms, which contradicts the scientific understanding of evolutionary biology.

3. **Evaluating the Truthfulness of Each Statement**:
- The assertion (A) is **true** because the earliest living organisms (prokaryotes) are indeed structurally simple.
- The reason (R) is **false** because the earliest living organisms were not more complex than present organisms; in fact, they were simpler.

4. **Conclusion**:
- Based on the evaluation, we conclude that the assertion is true while the reason is false. Therefore, the correct answer is that assertion is true and reason is false.

### Final Answer:
- **Assertion (A)** is true.
- **Reason (R)** is false.
- The correct option is: **Assertion is true and Reason is false.**