laxieqv
Some scientists have been critical of the laboratory tests conducted by the Federal Drug Administration on the grounds that the amounts of suspected carcinogens fed to animals
far exceeds those that humans could consume.
E. far exceed those that humans could consume
teaserbae
teaserbae , arriving at an answer through process of elimination is
an excellent method. (The best method, IMO.) Nice work, especially because these pronouns can be tricky.
If pronouns seem convoluted or unclear, replace the pronoun with what you think is the possible antecedent. Then decide whether the sentence makes sense.*
"Some scientists have been critical of the laboratory tests conducted by the FDA on the grounds that the amounts of suspected carcinogens fed to animals far exceed
those THE AMOUNTS
that humans could consume."
those in Option E is a pronoun referring to the antecedent
amounts (of carcinogens)
Until we do the substitution above,
that looks tricky. Afterwards, THAT should be much less confusing.
"That" connects "amounts" to "humans could consume." ("That" is a relative pronoun.)
If doubt still exists, test "that" by dropping the "that" clause.
If we strike "that humans could consume" we have
. . . the amounts of suspected carcinogens fed to animals far exceed [amounts]Shortened:
amounts far exceed amountsHuh?

That construction does not make any sense. Dropping the THAT clause produces nonsense.
In formal terms, "that" is a relative pronoun introducing a restrictive clause; the clause contains information we must have about "amounts."
Conclusion: "that" stays and E is indeed the correct answer. We're good.
Hope that helps.
*The sentence means: The FDA uses animals to test whether and at what level certain substances cause cancer. Some scientists have criticized the test results because the scientists believe that the tests do not replicate real conditions. The testers feed the animals huge amounts of the carcinogens -- amounts that are much higher than a human being actually could eat or drink.