Answer :
Answer: The correct answer for the blank is-
D) nuclear transfer.
Dolly was a female domestic sheep, and the first mammal that was cloned using an adult somatic cell ( particularly a mammary gland cell from a Finn Dorsett sheep). She was produced using a technique, which is termed as somatic cell nuclear transfer.
In this technique, the nucleus from an adult somatic cell was transferred to an unfertilized oocyte ( which was first enucleated that is nucleus was removed). After this, unfertlized egg was activated using electrical stimuli, which initiated cell division and produced Dolly.
Thus, option D) nuclear transfer is the right answer.