This question test our ability of grammatical construction. "by bathing the skin cells in extracts of immune cells" is a prepositional phrase (PP), so usage of that in underlined sentence is redundant. Similarly the main subject of clause should be Scientists / They.


Option-A & B - as explained above
Option-C : distort the meaning and passive form is unrequired
Option-D : Meaning error, 'as' is used for comparison, but not to indicate role/function, so it should be followed by clause
Option-E : Correct choice as the subject is they (scientist) and 'as' is used for comparison/reasoning.

in option E of the question, isn't pronoun "they" lead to logical predication error by acting as a potential antecedent to "scientists" and "human skin cells"? For different antecedents, different meanings are achieved, thus I think this option may be faulty.

Please help to clarify.