What Is/are the Challenges Facing Organ Regeneration Using Stem Cells

Multiple Choice

What is/are the challenges facing organ regeneration using stem cells?

A) Organs are highly complex,some containing many types of tissues,all of which would need to be assembled via regenerated tissues (stem cells) .
B) Organs are innervated;these connections are difficult to reassemble in regenerated organs.
C) It is difficult to get an engineered organ to function normally when transplanted.
D) We do not know all of the genes involved in regulating a cell,particularly stem cells.
E) All of the above.