Scientists say that, by bathing the skin cells in extracts of immune cells, that human skin cells in a test tube are made to behave as if they were immune system cells.

A. that human skin cells in a test tube are made to behave as if they were
B. that human skin cells were to behave in a test tube as if they were
C. human skin cells in a test tube were made to behave as if
D. they have made human skin cells in a test tube that were behaving as
E. they have made human skin cells in a test tube behave as if they were

E