Answer :

(a) They have the ability of self-renewal / to divide, and differentiate into any kind of cell/tissue/organ.
(b) – Inner cell mass of blastocyst / umbilical cord / Bone marrow.
(c) Diabetes treatment via forming islets of Langerhans,
Restoration of vision by injecting stem cells, to treat rheumatoid arthritis, reduces pancreatic cancer, to treat genetic disorder like cystic fibrosis, spinal cord injurie, heart disease, any other correct application.