When a certain insecticide is sprayed onto a given tree, the active

Choice E is NOT correct because the insects do not die because of ingesting the insecticide. Insecticides may be indirectly responsible, but the reason for death is NOT ingesting the insecticide.

Option D, though way too far-fetched, is the best answer. As discussed previously the "could be" scenario needs to be satisfied for a strengthening / weakening questions. (Scientifically there is a huge fallacy though - when the chemical evaporates and comes down with rain, the concentration of the chemical is way below the concentration when they are directly sprayed on the tree - it would be absurd that the rain falls only on the trees and nowhere else !)

What I dont catch is that how we can assume that a rainstorm has actually occurred?

+1 D
I agree with you; that "may" in the choice is tricky.
However, remember that you have to choose the best option among the choices, not the perfect one.
Additionally, remenber that you must accept the choices as true (Powerscore CR).

I agree with you in that I must accept the choices as true, but in order to weaken the conclusio, the answer should be:

Within 14 days after a tree is sprayed, a rainstorms carried the insecticide into a nearby stream, preserving the activity of its chemicals until it evaporates into the atmosphere and precipitates down with the rain.

Otherwise, you have to assume too much. Imagine that the tree is located in a city where never rains.

I was stuck between C and D. Why not C?

Here is the OE; however, I am still not able to comprehend reason for eliminating option E. Can someone please help.


OE:

The author of this argument concludes that, because an active chemical in an insecticide becomes inactive after 14 days of air exposure, the death of an insect that lands on a sprayed tree is not due to the ingestion of this insecticide.

The answer must provide evidence against the following chain of events: Insecticide is sprayed, active chemical is exposed to the air, 14 days pass, chemical becomes inactive, insect's death is not due to this pesticide.

Choice D is correct. It provides evidence that the chemical, once sprayed, is not necessarily exposed to the air for fourteen continuous days. If a rainstorm can carry the insecticide into a stream and preserve its activity, it is not until the chemical is re-exposed to the air that its activity resumes. Thus, this chemical could evaporate, rain back down onto the tree, and cause the death of an insect outside of the 14-day window. This weakens the argument.

Choice A is outside the scope of the argument, which is concerned with the effect of this insecticide on an insect.

Choice B is irrelevant; there is no evidence that the amount of insecticide has any effect on how long it remains effective. After 14 days, all the insecticide, no matter how much there is, should become inactive and non-lethal.

Choice C is about an irrelevant group of insects; the conclusion is that insects that land on the tree do not die from ingesting this insecticide; the insect eggs inside the tree are out of the scope of this argument.

Choice E is irrelevant to the conclusion. This choice states that the insecticide might have another lethal effect on insects, causing them to die from malnutrition. However, the argument states explicitly that insects that land after 14 days do not die from ingesting the insecticide. This choice actually strengthens that argument, by offering another reason that the insects might have died on this tree.

Choice D is irrelevant, it is talking about rainstorm and has got more assumptions like rain has to come, insecticide has to be carried away and insecticide should get percipitated and again rain has to come in the same place.


Choice E: Clearly says even after 14 days insecticide kills insects in different way on the same tree for the same insects that survived with in 14 days.

When a certain insecticide is sprayed onto a given tree, the active chemical in this insecticide becomes inactive, and non-lethal to insects, after being exposed to the air for 14 days. This chemical becomes active as soon as a tree is sprayed and is no longer considered active as soon as it is ingested by an insect, which dies immediately upon this ingestion. Therefore, the large number of insects that have been observed to die after landing on a tree more than 14 days after this tree has been sprayed must not have died from ingesting the insecticide.

Which of the following, if true, most seriously weakens the conclusion above?

A) Some laws about insecticide use do not ban the use of several insecticides at a given time, as long as these insecticides are not sprayed simultaneously.

B) Machines, which are often used to spray an insecticide the first time this insecticide is used in a given region, often spray more insecticide than is necessary to kill the insects on any given tree.

C) The insecticide can slowly penetrate the bark of a tree and poison any insect eggs lain inside, preventing these eggs from hatching for more than 14 days after the initial insecticide spraying.

D) Within 14 days after a tree is sprayed, rainstorms may carry the insecticide into a nearby stream, preserving the activity of its chemicals until it evaporates into the atmosphere and precipitates down with the rain.

E) This insecticide can cause leaf dehydration, which sucks the nutrients out of the leaves, causing insects that depend on the tree for nourishment to die.

I don't understand the confusion with D) it is very clearly the answer and not just because it is the best answer, it has nothing wrong attached to it.
For those saying "MAY" is a little far fetched - it is definitely not it is a proposed theory and hence the writing style also even if it CARRIES THE INSECTICIDE TO THE STREAM SOMETIMES it still holds it value because the question does not say IN ALL THE CASES AT ALL TIMES, it is just concerned with the explanation of why the phenomenon would happen.