The correct answer is "Both A and R are true, and R is the correct explanation of A."

Explanation:

- Assertion (A) states that insect-resistant transgenic cotton has been produced by inserting the Bt gene. Bt stands for Bacillus thuringiensis, which is a bacterium that produces a protein toxic to certain insect pests. By inserting the Bt gene into cotton plants, they can produce this insecticidal protein and become resistant to specific insect pests.

- Reason (R) states that the Bt gene is derived from a bacterium. This is true as the Bt gene is sourced from Bacillus thuringiensis, a naturally occurring soil bacterium that produces the insecticidal protein. The gene responsible for producing this protein can be isolated and inserted into the genome of other plants, such as cotton, to confer insect resistance.

Therefore, both Assertion (A) and Reason (R) are true, and Reason (R) provides the correct explanation for Assertion (A).