MEDICAL RESEARCH AT THE CELLULAR LEVEL, ____ RESEARCH ON THE IMMUNE SYSTEM, HAS BEEN MADE POSSIBLE THROUGH TWENTIETH-CENTURY ADVANCES IN TECHNIQUES OF GENETIC RESEARCH
28. Medical research at the cellular level, ____ research on the immune system, has been made possible through
twentieth-century advances in techniques of genetic research.
A. which
B. Whereas
C. such as
D. is also