Understanding the argument -
Environmentalist: When bacteria degrade household cleaning products, vapors that are toxic to humans are produced. Fact. It says vapors are produced. Ok, so when are they produced? When bacteria degrades household products. Got it. This means that vapors are not always produced, but they are produced when bacteria degrade household products. ok. so what kind of vapors are we talking about? Some general? No. The ones that are toxic to humans. ok. Keep this meaning in mind.
Unfortunately, household cleaning products are often found in landfills. - Fact. But how about bacteria? Are bacteria also found in landfills? If not, then the vapors will not be produced. So we don't know yet.
Thus, the common practice of converting landfills into public parks is damaging human health. - Conclusion. Oh ok. So, in the first statement, the author gave some relationships that entail the presence of some household cleaning products + bacteria that produce harmful vapors. But then, in the 2nd statement, the author gave a scenario of landfills where household cleaning products are present. But bacteria, we don't know. Then, the author concluded that as household products were present in the landfills, the parks built by converting landfills to parks are damaging health. But isn't it ridiculous? We don't even know if we have the required bacteria in the landfill to convert these household cleaning products into vapors. So, knowing whether bacteria are present is an essential missing or minimum information to conclude. Without that, it's just that if we 1+a = 2. So "a" has to be 1. Else, we can't say that 1+a is 2. Isnt it? Let's look at options now.
Option Elimination -
(A) In at least some landfills that have been converted into public parks there are bacteria that degrade household cleaning products. - ok. This bridges the gap of "bacteria."
(B) Converting a landfill into a public park will cause no damage to human health unless toxic vapors are produced in that landfill and humans are exposed to them. - This essentially says X unless Y, which means Y is the necessary condition for not X, Meaning that the toxic vapor production is a necessary or a minimum condition for damage to human health. But that we already know from the argument. But what we don't know is whether "bacteria" is present or not. If, for example, there are no bacteria, the conclusion doesn't hold. So, this information repeats what we already know. Finding assumptions is about finding a minimum condition or missing premise and not about restating what's already stated or implied in the argument. Wrong.
(C) If a practice involves the exposure of humans to vapors from household cleaning products, then it causes at least some damage to human health. - Again, we know it already, but we don't know if the "bacteria" is present. Wrong.
(D) When landfills are converted to public parks, measures could be taken that would prevent people using the parks from being exposed to toxic vapors. - What is an assumption? Missing premise? Right? What is a premise? A fact? Right? But what is this statement? An opinion. How can this be our assumption? This is a distortion. The author tries to create some options using familiar words from the argument to confuse us.
(E) If vapors toxic to humans are produced by the degradation of household cleaning products by bacteria in any landfill, then the health of at least some humans will suffer. - We know it from the argument. But what we don't know is whether bacteria is there or not. This option states if the blah blah.....we don't need if conditional; we need a simple confirmation that bacteria exists as A does. Simple. No roundabouts, please, which is what this option does. Distortion.