Which of these is the BEST source of stem cells and minimizes the risk associated with stem cell transplantation?(Please Help!!)

Select one:
a. Stem cells from rejected grafts that initiated an immune response.
b. Stem cells preserved from the umbilical cord of the person.
c. Stem cells from a donor having the same blood group.
d. Stem cells from a donor who is the same age as the patient.

It is believed that europa, one of jupiter’s moons has an ocean beneath its surface. based on how earth’s oceans and atmosphere are believed to have formed, what can be said about europa’s supposed ocean? the arrival of in the early days of europa’s existence could have formed its ocean. it is likely that the water experienced , similar to earth. it is also possible that this water is retained beneath europa’s surface and in its atmosphere due to europa’s .