Sentence Correction

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

I was confused between D and E. And in option E, there are two "they"s that refer to two different antecedent.