Answer:
A.) A fertilized egg cell
Step-by-step explanation:
Most specialized cells in the body don't transform into any other type of cell after they become specialized. This because each type of cell is highly specific and different between each other. A fertilized egg cell is the exception, as this type of cell can actually become any other type of cell in order to form the organisms. It is a specific ability for this kind of cell and once it is transformed into other type of cell it cannot go back. Because of this characteristic, this kind of cell is being used in research for regenerative medicine.