Critical Reasoning

A fatal disease caused by the parasite Encarsia formosa and spread by greenhouse whiteflies has already killed 50 percent of the cucumber crops planted on the Redfern farm, the largest cucumber producing farm in the northeastern United States. Trialeurodes vaporariorum kills the larvae of greenhouse whiteflies. In an effort to save the remaining cucumber crops on the farm, plant biologists plan to introduce Trialeurodes vaporariorum to the cucumber fields of Redfern farm.

Which of the following, if true about Trialeurodes vaporariorum, provides the strongest evidence that the plan will succeed?

(A) It is spread by a type of earthworm that lives on the farm near greenhouse whiteflies' hatching sites.
(B) It has been known to lay dormant in cucumber plants for five years or more before it begins to reproduce.
(C) It spreads more slowly than Encarsia formosa under most conditions.
(D) It does not destroy some commonly found subspecies of greenhouse whiteflies.
(E) It has been known to kill wheat and barley crops by attacking their nutrient intake capabilities

OA A but i don't agree

Plan - to save rest of the cucumber crops, please introduce Trialeurodes vaporariorum to the cucumber fields of Redfern farm

Choice A describes one of the ways of spreading Trialeurodes vaporariorum....how does that provide evidence that the plan will succeed???

Evidence, here, can be provided only through similar case studies...the argument, otherwise, is solid. can we discuss the efficacy of this Q??

Trialeurodes vaporariorum kills the larvae of greenhouse whiteflies. Plant biologists plan to introduce Trialeurodes vaporariorum to the cucumber fields of Redfern farm.

Which of the following, if true about Trialeurodes vaporariorum, provides the strongest evidence that the plan will succeed? (choices are about TV...not about Encarsia)

(A) It is spread by a type of earthworm that lives on the farm near greenhouse whiteflies' hatching sites. (earthworm which spreads TV resides near whiteflies hatching sites...they have high chances of being effective) correct
(B) It has been known to lay dormant in cucumber plants for five years or more before it begins to reproduce. (we are not sure whether TV has already spent 5 yrs ...if it will be effective if it has already spent otherwise not.
(C) It spreads more slowly than Encarsia formosa under most conditions. (what if one TV kills many more Encarsia...if that is so, it does not matter whether it spreads slower than encarsia)
(D) It does not destroy some commonly found subspecies of greenhouse whiteflies. (we are concerned with greenhouse whiteflies only...even if we are concerned...this choice weaken)
(E) It has been known to kill wheat and barley crops by attacking their nutrient intake capabilities (we are concerned with cucumber only)

Feel OA is correct. Lets discuss

No other option provided other than the OA strengthen the argument.This is my resoning

(A) It is spread by a type of earthworm that lives on the farm near greenhouse whiteflies' hatching sites.

(B) It has been known to lay dormant in cucumber plants for five years or more before it begins to reproduce.--As already half of the plants are effected in Redfern farm it needs an immediate action,but this shows that application of Trialeurodes vaporariorum need 5 years to take effect--wakening hence incorrect


(C) It spreads more slowly than Encarsia formosa under most conditions.--if Trialeurodes vaporariorum spreads more slowly than Encarsia formosa then it will not be effective for the prevention of Encarsia formosa--wakening hence incorrect

(D) It does not destroy some commonly found subspecies of greenhouse whiteflies.--if Trialeurodes vaporariorum cannot destroy some commonly found subspecies of the primary carrier then it will not be effective for the prevention of Encarsia formosa--wakening hence incorrect

(E) It has been known to kill wheat and barley crops by attacking their nutrient intake capabilities --argument is about cucumber not about wheat and barley crops--irrelevent hence incorrect

The official answer to this question, A, is correct for exactly the reason that pnk notes: it provides an additional fact that adds to the efficacy of the plan. If worms spread TV right where whiteflies live, then it becomes more likely (at least a bit) that the TV added to the farm will be spread to the whiteflies. Because we are given factual evidence in the argument that TV kills the larvae of whiteflies, this should kill the whiteflies and save the cucumbers. Is this plan foolproof- not at all! But it is MORE likely to succeed because of this additional fact.

Your qualm, liferocks, has to do with the GMAT's definition of the word "evidence." On the GMAT, evidence has a very different meaning than it has in a scientific experiment or a court case. It simply means something that is FACTUAL in the world of the question. So, in this question, the FACT that earthworms spread TV would certainly be considered a piece of "evidence" by the GMAT writers.

By the way, the other elements of the argument, assumptions and conclusions, are not factual; they are opinions in the argument, either stated or unstated. For example, in this argument, the conclusion the biologists make is that introducing TV will help save the remaining cucumber crops. And there are many (some say, infinite) assumptions inherent to this, and any argument. The plant biologists assume that the TV introduced into Redfern farms will reach and kill the flies, that these particular flies are not immune to TV, that cucumber crops will not be themselves killed by TV, and so on. These are assumptions held (but not stated explicitly) by the plant biologists in the question.

Hope this helps! We at Knewton pride ourselves on the reliability and extreme test-like nature of our questions. This is a prime example, and we hope that it provides a good teaching moment!

This is a valid GMAT question: I remember a similar one among the official practice questions.