So I am watching the Webinar on Weakening and Strengthening questions and I have a questions about the first question. The first question is a strengthening question and I have typed the stimulus and answer choices below.
Stimulus: Several years ago, as a measure to reduce the population of gypsy moths, which depended on oak leaves for food, entomologists introduced into many oak forests a species of fungus that is poisonous to gypsy moth caterpillars. Since then, the population of both caterpillars and adult moths has significantly declined in those areas. Entomologists have concluded that the decline is attributable to the presence of poisonous fungus.
A. A strain of gypsy moths whose caterpillars are unaffected by the fungus has increased its share of the total gypsy population.
B. The fungus that was introduced to control the gypsy moth population is poisonous to few insect species other than the gypsy moth.
C. An increase in numbers of both gypsy moth caterpillars and gypsy moth adults followed a drop in the number of some of the species that prey on the moths.
D. In the past several years, air pollution and acid rain have been responsible for substantial decline in oak tree populations
E. The current decline in gypsy moth population in forests where the fungus was introduced is no greater than a decline that occurred concurrently in other forests. (I thought that this was the answer.)
Questions
I know that with strengthening questions you are looking for the answer choice that strengthens the argument and blocks the alternative. I am a little confused on what exactly does it mean to block the alternative. After looking at the explanation of the webinar video for this question it seems as if blocking the alternative is an answer choice that provides another alternative. Is that correct? I believe that the whole concept of "blocking the alternative" is going over my head and I would like further clarification on this strategy. In addition, can someone explain how A strengthens the argument....A does not seem like it supports thew conclusion if the conclusion is saying that the fungus contributes to the decline of moths and A is talking about that the population increased.