This is an easy one. For real test takers, the question should not create any possible concerns need a reason to explain us that the farmers are telling the truth.

The price increase is due to maybe a heavy drought, or some other reason that cuts the production and therefore we do have a shortage.

B says exactly this

A is completely out of scope. We need to find out a valid reason WHY we do have a real shortage in the harvesting of syrup

Regards

The price of maple syrup has jumped from 22 dollars a gallon three years ago to 40 dollars a gallon today. It can be concluded that maple-syrup harvesters have been artificially inflating prices and that governmental price regulations are necessary to control rising prices.

Which of the following, if true, casts the most doubt on the conclusion drawn above?


Conclusion

maple-syrup harvesters have been artificially inflating prices and that governmental price regulations are necessary to control rising prices.

To weaken this conclusion, we should look for an evidence which provides natural reasons or non-artificial reasons for the prices to go up.

Choice B provides such an evidence and is therefore the correct answer.

(B) Insect infestation and drought have stunted the growth of syrup-producing maple trees and caused less-abundant syrup harvests.

Lets look at the choices

(A) The government already requires maple-syrup harvesters to submit their facilities to licensing by the health department.

This government requirement does not prove or disprove that prices were artificially inflated. So we reject it.

(B) Insect infestation and drought have stunted the growth of syrup-producing maple trees and caused less-abundant syrup harvests.

If insect infestation and drought have caused less-abundant syrup harvests, then this provides an excellent explanation for the jump in prices from dollars to 40 dollars, due to reduced supplies attempting to meet prevailing or greater demands. So we retain this.

(C) Maple syrup is produced in rural areas that suffer from high unemployment.

If there is high unemployment in rural areas where Maple syrup is manufactured, then labour should be available at cheaper costs, bringing down prices of Maple syrup. But prices have gone up, proving that prices have gone up artificially. This strengthens the argument. So we reject this choice.

(D) Technological improvements in maple-syrup harvesting have reduced production costs.

If technological improvements have reduced production costs, then it proves that prices have been raised artificially by Maple-syrup harvesters. This strengthens the argument. So we reject this choice.

(E) Maple-syrup prices have risen many times in the past, though never before at the rate recently observed.

This fact that Maple-syrup prices have risen many times in the past and rates different than now, neither proves nor disproves that the prices have been inflated artificially. So we reject this.

Therefore, Choice B is the correct answer.