This doesn’t help establish that only government-sponsored research investigates these techniques. (A) tells us that the government does at least some of this research, but we don’t know whether there could be other sources that also do this research.

This doesn’t help establish what kinds of entities research agricultural techniques and whether governments are the only ones who will research techniques that are unlikely to lead to marketable products.

This strengthens the argument by limiting the potential entities that conduct research to, in most cases, private for-profit corporations and the government. Since the premises already eliminate private corporations as a source of research, we’re left with the government.

The argument is concerned with research into techniques that don’t use commercial products. Which entities research the techniques that do use commercial products has no impact on the reasoning.

This doesn’t help show that research investigating agricultural techniques that don’t use commercial products is exclusively done by the government. (E) leaves open the possibility that non-government entities also do a lot of this research.