Good question. "Could consume" is in the indicative tense, which is actually preferred in this case. The meaning of the sentence is that we feed animals more carcinogens than humans are able to consume. "Consume" is in that indicative tense (e.g. Humans consume vegetables - no need for past or future...it just happens regardless of time), and "could" adds that conditional "able to". It's not noteworthy that animals consume more chemicals than we DO consume...it's noteworthy that we give them more than we could (ever) consume - there's that element of impossibility that makes it a noteworthy sentence.
While down between D and E, I'd say that they both say the same thing, but that E says it much more directly.