A certain strain of bacteria was found in the stomachs of ulcer patien

My view over it.

x causes y.
no y , no x.

E goes with that logic.

GMATNinja ChiranjeevSingh , while E may be tempting but how does it strengthen the argument ? 2000 people is a large number but definitely we may not be sure . in B we know that there were any other serious health problems after ingesting bacteria strain so it makes it clear that only ulcers might have been there right ?

We aren't looking for an answer choice that PROVES that the argument is correct. Instead, we're looking for the choice that most supports the argument.

If some of those 2000 people did in fact have the bacteria strain in their stomachs, it would be easy to discredit the argument -- that would be clear evidence that having the bacteria does not necessarily mean having ulcers. That might not DISPROVE the argument, but it would certainly be strong evidence against the argument.

But since none of those 2000 had the bacteria strain, (E) gives us solid evidence that no bacteria strain means no ulcers -- and that supports the idea that the bacteria strain is in fact the cause of the ulcers.

All (B) tells us is that the researcher did not develop any other serious health problems. But it doesn't tell us what caused the ulcer! Maybe the bacteria caused the ulcer, but maybe something else caused the ulcer. Whatever did cause the ulcer didn't cause any other serious health problems, but that doesn't help us assess the actual cause of the ulcer.

(B) doesn't help (or hurt) the argument. Even though (E) doesn't PROVE that the argument is true, it certainly supports the argument and is therefore a better answer.­

I hope that helps!

­Thanks for the explanation. It's a difficult question IMO .