The problem with this study is that it uses chemical scents, while sulfur is natural.

How can the author make a broad claim about sulfur weakening the sense of smell in general, if the scents in the study are chemically reproduced? What about natural fragrances? A hole in the argument: what if sulfur improves your perception of natural scents?

So,

a. The chemicals used in the study closely but not perfectly reproduced the corresponding natural scents.

Would, in fact, strengthen the argument.

All the others weaken the argument when you work through them.

@EthanLarson LOL

Hi guys! I had an easy way of understanding this.

You simply need to understand what the premise is and what the conclusion is, since the question asks about what tracks the conclusion logically.

(I recommend that if you don't know what the premise is and what the conclusion is, just think what supports the main idea. This is the premise.)

The conclusion is the last sentence in this case. So, whatever answer we choose needs to correlate to "most" of the drinking water becoming polluted.

While both E addresses most of the drinking water in the valley becoming polluted too, D is the correct answer, because E grossly talks about "none" of the large dairies meeting federal drinking standards (that's preposterous, the text clearly says "most", and there is no reason to assume "none" will meet federal standards).

D addresses most of the polluted drinking water and is accurate in its portrayal of the text.