The proposed answer makes no sense - it assumes that Q will be used for the first 30 days and P for the subsequent period. If P can be reapplied indefinitely without damaging a crop, while Q can only be used for the first 30 days, why are we assuming both will be used. Why can't P be used for the entirety of the period?

As for the OE, which mentions Q's harmless nature towards humans, following that logic would mean that it could still be used in lieu of P for certain crops because P does not yield output that is fit for human consumptions, while Q does. If anything, option C is slightly supported.

Undermines the argument meaning we need to find an option where Instecticide Q have some uses which is in contrary mentioned in passage. So I believe option A is correct.

Please explain

Insecticide Q is noteworthy both for its control of pests that attack crops and its benignity toward humans.


Ok: here we have a double benefit of the chemical

However, its effects only last 30 days, a period insufficient to protect any major crop until harvest, and reapplication of Insecticide Q usually kills the crop.

here we do have a downside: only one month the protection lasts and a reapplication would kill the crop. USUALLY

Insecticide P, on the other hand, can be reapplied indefinitely without damaging the crop. Therefore, Insecticide Q has no discernible use in the protection of major crops.

Ok. The P compound instead can be reapplied indefinitely but maybe in the first 30 days does not have the same positive effects. We do not know. Therefore, Q is not usable according with the argument

We need to find an option that tells us P has some flaw or that Q is useful indeed. Notice how therefore indicates us the conclusion of the argument and this is what we must attack


Which of the following, if true, most seriously undermines the argument?

A) There are several minor crops that can be harvested in as few as 20 days.

This option does not tell us anything of useful. The fact that minor crops can be harvested before the month not indicate something about if Q is good or not. we already know that Q lasts for 30 days. Moreover, it is not specified IF this is the first or the second application or else

B) A third insecticide not mentioned in the passage protects crops better than either Insecticide Q or P.

Completely OFF as an option. A third compound is NOT what we are looking for to undermine the argument itself

C) Foods treated with Insecticide P are often banned from organic markets.

Stupid option. We need to find something related to the treatment of the crops NOT the banning of food

D) Both Insecticides Q and P can be used on the same crop.

This tells us that Q is useful and effective. For example: we can use it in the first month to protect the crop and THEN use P for a reapplication until we harvest the crop BOTh on the same plant and also both are not harmful for humans. Sooo Q is any good, contrary to our conclusion

E) The production of Insecticide P, once economical, has recently tripled in cost.

Irrelevant

I hope this helps

Carcass
so the argument is "Insecticide P, on the other hand, can be reapplied indefinitely without damaging the crop. Therefore, Insecticide Q has no discernible use in the protection of major crops."
here i initially thought that nothing more is given about P so i need to find something that weakens the position of the insecticide P
option C looked correct but later i realized that *wait, it essentially mentioned that P has one additional benefit over Q, so then that means i need to find an option that weakens the stand that Q and P can both be used*
is this how it supposed to be?

did you read my explanation just above which is quite picky?

What is still unclear sir ? I did not get in full

i do understand it
but here's my argument. if P can be used instead of Q after 30 days then why use Q to begin with
we can just use P right from the start.
if this is true then that means, we need to find something that works against P

Also, I do think you went to far. Always the argument must be considered as it is provided. You objection could be reasonable but it is out of scope for the reason in the quote