Doctors hope that one day the body's master cells, called stem
cells, can be directed to grow in organs or tissues appropriate for
transplant, use them to test drugs and potentially toxic chemicals,
and may study them to gain insight into basic human biology.
A. transplant, use them to test drugs and potentially toxic
chemicals, and may study them
B. transplant, using them to test drugs and potentially toxic
chemicals, and studied.
C. Transplant, used to test drugs and potentially toxic chemicals,
and studied.
D. A transplant, use them for testing drugs and potentially toxic
chemicals, and for studying.
E. A transplant, used to test drugs and potentially toxic chemicals,
and may study them.
[spoiler]A/C[/spoiler]