[A]: lnterspecific mating often produces a more vigorous but sterile `F_1` hybrids.
[R]: Reproductive isolation does not let evolution to occur.

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 Interspecific Mating**:
- Interspecific mating refers to the mating or crossing between individuals of different species but within the same genus. This can lead to the production of hybrids.

**Hint**: Remember that interspecific mating involves different species but they must belong to the same genus.

2. **Characteristics of F1 Hybrids**:
- The assertion states that interspecific mating often produces vigorous but sterile F1 hybrids. This means that while the hybrids may be strong and healthy, they are unable to reproduce.

**Hint**: Focus on the terms "vigorous" and "sterile" when considering the characteristics of the hybrids.

3. **Example of Interspecific Hybrid**:
- A common example of an interspecific hybrid is the mule, which is produced by crossing a female horse and a male donkey. Mules are typically robust but sterile, meaning they cannot produce offspring.

**Hint**: Use the mule example to illustrate the concept of sterile hybrids from interspecific mating.

4. **Evaluating the Assertion**:
- The assertion is true because interspecific mating does indeed produce vigorous but sterile hybrids.

**Hint**: Confirm that the assertion aligns with the definition and examples discussed.

5. **Understanding Reproductive Isolation**:
- The reason states that reproductive isolation does not let evolution occur. Reproductive isolation is the inability of a species to breed successfully with closely related species due to various barriers (geographical, behavioral, physiological, genetic).

**Hint**: Identify the factors that contribute to reproductive isolation.

6. **Evaluating the Reason**:
- The statement that reproductive isolation does not let evolution occur is incorrect. While reproductive isolation prevents certain species from interbreeding, it does not stop evolution, which is the change in species over generations.

**Hint**: Differentiate between reproductive isolation and the concept of evolution.

7. **Final Conclusion**:
- Since the assertion is true and the reason is false, the correct answer is that A is true, and R is false.

**Hint**: Look for the option that matches the evaluation of both A and R to select the correct answer.

### Summary of the Answer:
- The correct answer is that the assertion (A) is true and the reason (R) is false.