The correct answer is option 3: A is true, but R is false. Dolly, indeed, was the first cloned mammal, which makes assertion (A) true. However, the reason (R), stating that Dolly was produced by in vitro fertilization, is false.

Dolly was produced using a technique called Somatic Cell Nuclear Transfer (SCNT). In this process, the nucleus of an egg cell was removed and replaced with the nucleus of a somatic (body) cell from another adult individual. Then, the egg was stimulated to divide, forming an embryo that was identical to the organism that donated the somatic cell. The embryo was then implanted into a surrogate mother.

In vitro fertilization is a different process wherein an egg is fertilised by sperm outside the body. Therefore, this is not the technique used to produce Dolly. Hence, option 3 is the correct answer.

Alert - correct answer should be option 3.