This tells us that if reducing agricultural production increases biodiversity, then we should reduce agricultural production. But we’re trying to prove that sustaining growth, which requires increasing agricultural production, requires abandoning conventional agriculture. So the conclusion concerns a situation in which increasing agricultural production is required. A principle about when we should reduce agricultural production doesn’t strengthen the argument.

This helps establish that if we sustain economic growth, we should radically change our agricultural techniques. We know from the premises that sustaining economic growth while at the same time not reducing biodiversity requires abandoning conventional agriculture. According to (B), if we sustain economic growth, we should not reduce biodiversity. So it follows that if we sustain economic growth — which (B) establishes should be accompanied by our desire not to reduce biodiversity — then that requires abandoning conventional agriculture.

This doesn’t tell us anything about not reducing biodiversity. So it doesn’t give us any information that would help connect sustaining economic growth to abandoning conventional agriculture.

If (D) were true, that leaves open the possibility that agricultural production could be more important than preserving biodiversity. And that opens the possibility that we might not need to abandon conventional agriculture in order to sustain economic growth. Maybe we can sustain economic growth and be OK with reducing biodiversity? In that case, the premise about abandoning conventional agriculture doesn’t trigger. (D) doesn’t help show why sustaining economic growth does require abandoning conventional agriculture.

(E) tells us about a necessary condition (”only if”) in order for it to be appropriate to radically modify agricultural techniques. But that would only allow us to prove when we should NOT radically modify techniques. It doesn’t help us prove that sustaining economic growth requires us to radically modify techniques.