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

Ans: C