This argument begins with a premise stating thatnormallyit takes a cake a week to become moldy in a refrigerator. The next premise is thatthis particularcake is moldy. The argument concludes that this particular cake must have been in the refrigerator for at least a week.
The conclusion depends on the idea that this cake has been aging normally inside the refrigerator. (If the refrigerator were defective, or the cake were abnormally perishable, the conclusion would be undermined.) To strengthen the conclusion, you should look for a statement that indicates that the cake has indeed been aging inside the refrigerator in the normal fashion.
(A) Weaken. If Rahul's refrigerator is dirty, the cake may well have gotten moldy unusually fast - which means the cake could be less than a week old.
(B) Weaken. If a lack of electricity has kept the refrigerator from working, the cake may well have gotten moldy unusually fast -- which means the cake could be less than a week old.
(C) CORRECT.Strengthen. If the cake hadnotbeen fresh when it was placed in the refrigerator, or if it hadnotbeen in the refrigerator continuously since then, it might have gotten moldy in less than a week. Therefore, knowing that the cake was fresh when it was placed in the refrigerator, and that it has been there ever since, gives us reason to think that the cake has been aging in the refrigerator at a normal rate.
(D) Irrelevant. This study only provides evidence to support the initial premise in the argument, namely, that "normally it takes a week for a cake to become moldy in a refrigerator." This answer choice does not state whether or notRahul'srefrigerator is among the 95%; nor do we know anything else about this specific situation.
(E) Irrelevant. The cake may have been baked on a Thursday -- but was it the most recent Thursday, or some Thursday last year?