The only known source of human embryonic stem cells is:

A) placental tissue
B) umbilical cords
C) early human embryos
D) brain tissue
E) nerve tissue

Human Embryonic

Relating to the early stages of human development within the womb, from conception to the eighth week of pregnancy.

Stem Cells

Undifferentiated cells capable of giving rise to indefinitely more cells of the same type and from which certain other kinds of cell arise by differentiation.

Placental Tissue

Tissue part of the placenta, which supports fetal development by facilitating nutrient uptake, waste elimination, and gas exchange between mother and fetus.