In the context of recent advances in human reproductive technology. "Pronuclear Transfer" is used for

1. A

   fertilization of egg in vitro by the donor sperm

   IVF with donor sperm. Ordinary IVF, not pronuclear transfer.

2. B

   genetic modification of sperm producing cells

   Genetic modification of spermatogonia. Different technique.

3. C

   development of stem cells into functional embryos

   Stem cells to embryos. Not PNT.

4. D

   prevention of mitochondrial diseases in offspring

   Prevention of mitochondrial disease. Pronuclear transfer moves nuclear DNA into a donor egg with healthy mitochondria.

Summary. Official key is (d). Pronuclear transfer is a mitochondrial-replacement method: the zygote’s pronuclei are moved into an enucleated donor zygote so the child does not inherit mutant mtDNA.