There is no other way to solve this question other than POE. The answer is E.
Dissecting the sentence into meaningful phrases.
The federal rules | ..... | were established to ensure that patients | ...... | and | ..... | evaluate the experiment before it was conducted.
Prephrased correct answer - [to ensure that patients] are warned | .... | [and] | that an independent panel would | .....
So as we see, we need a verb that makes good sense after 'patients', we need 'that' after 'and' and another verb after 'panel'.
Option E is the only logical answer, other options do not conform to the prephrased correct answer format. So E only remains as the best among the answer options, although, grammatically it is still not the perfect answer.
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