Here we're trying to strengthen a prediction - a very common conclusion type on the GMAT. Let's start by talking about predictions in general.pradeepkaushal9518 wrote:A certain variety of spear thistle, a weed that quickly spreads across grasslands, was inadvertently introduced into Canada from the United Kingdom in the late 1960's. This weed takes nutrients and moisture from the soil that would otherwise go to timothy grass, the most common Canadian grass varietal. To help track the spread of spear thistle, the Canadian government has released a fact sheet to farmers to help them identify the weed-the fact sheets contain pictures of the weed and explain its effect on soil; the sheets also ask farmers to report any outgrowths of the weed found on their land.
Which of the following, if true, would provide the most support for the prediction that the agencies' action will have its intended effect?
(A) The spear thistle is one of several foreign weed species that draws nutrients from the soil of Canadian farmers.
(B) The animals that graze on timothy grass on Canadian farms are uninterested in eating spear thistle because of its thorns.
(C) The spear thistle leaves spiny thorns on the ground which can poke holes in timothy grass.
(D) Spear thistles usually draw nutrients out of the soil at night, but timothy grass usually grows during the daytime hours.
(E) Most Canadian farmers use timothy grass as the main varietal with which to feed and nourish their livestock.
A prediction is speculation about the future. Whenever an author makes a prediction, she makes one general assumption:
Nothing unexpected has happened/will happen to prevent the prediction from coming true.
To strengthen a prediction, we look for a statement that either flatly says that nothing new and unexpected has happened or, more often, that eliminates a potential obstacle to the prediction coming true.
To weaken a prediction, we look for something that the author didn't anticipate that creates a potential obstacle to the prediction coming true.
Since this is a "strengthen the prediction" question, we should:
1) Identify what the prediction is; and
2) look for an answer that removes a potential obstacle.
In this question we get the prediction in the stem, not the stimulus. Per the question, the prediction is "the agency's action will have its intended effect". Now we need to go to the stimulus to identify what the intended effect is; we find it at the beginning of the final sentence: "to help track the spread of spear thistle".
Our prediction: the correct answer will remove a reason why the plan would NOT help track the spread of the thistle.
a) do we care how many foreign weeds there are? Nope - outside the scope, eliminate.
b) do we care if animals eat the thistle? Yes! If animals ate all the thistle, then farmers wouldn't be able to track it. Since (b) tells us that animals are NOT eating the thistle, it removes a potential obstacle and is therefore a valid strengthener. choose (b)!
On test day we should be confident and stop right there. In practice, you should always review every choice to learn more about the common wrong answers on the GMAT. Let's go into "review mode" and look at the remaining choices.
c) do we care if the thistle pokes holes in grass? Nope - outside the scope, eliminate.
d) do we care about when each plant feeds? Nope - the different timing has no impact on the farmers' ability to spot the weeds - eliminate.
(If, on the other hand, (d) told us that the thistles hibernate during the day and are only visible at night, it would be a weakener.)
e) do we care that most Canadian farmers use timothy grass to feed their livestock? Nope - we're not given any link between the existence of timothy grass and the spear thistle - we're only told that the thistle competes with timothy grass for the same nutrients. Whether or not the grass exists on most farms is irrelevant - and how Canadian farmers use the grass is even more irrelevant.
Let's use Kaplan's denial test on (b) and (e) to better illustrate why (b) is correct and (e) is irrelevant.
Denial of (b): the animals that graze on timothy grass eat the spear thistle. Well, if the animals are eating it, then there won't be any for the farmers to identify. The denial of (b) weakens the argument, so (b) must strengthen.
Denial of (e): less than half of Canadian farmers use timothy grass as the main varietal with which to feed and nourish their livestock. If only 49% (a statistic consistent with the denial of (e)) of Canadian farmers use timothy grass, does that weaken the argument? What if 100% of farms were covered in timothy grass, but most used it as their secondary form of feed for livestock (also consistent with the denial of (e)) - would that weaken the argument? Since the answer to both questions is "no", the denial of (e) is NOT a weakener; accordingly, (e) is NOT a strengthener.
