One of the Major Impediments of Successful Full Recovery of Function

One of the major impediments of successful full recovery of function following implantation of neural stem cells is that

A) such a strategy works only for physical trauma-based damage (e.g., spinal cord injury) , rather than for neurodegenerative diseases (e.g., Alzheimer's) .
B) such a strategy works only for neurodegenerative diseases (e.g., Alzheimer's) , rather than for physical trauma-based damage (e.g., spinal cord injury) .
C) often, neural stem cells fail to adapt to their new host environment.
D) often, the compromised host environment can affect the graft of the stem cells, disabling the latter.
E) neural stem cells must be of the correct phenotype.