I got a PM on this one...
Here is the text of the question in the file:
Purebred dogs are prone to genetically determined abnormalities. Although such abnormalities often can be corrected by surgery, the cost can reach several thousand dollars. Since nonpurebred dogs rarely suffer from genetically determined abnormalities, potential dog owners who want to reduce the risk of incurring costly medical bills for their pets would be well advised to choose nonpurebred dogs.
Which one of the following, if true, most seriously
weakens the argument?
(A) Most genetically determined abnormalities in
dogs do not seriously affect a dog's general
well-being.
(B) All dogs, whether purebred or nonpurebred,
are subject to the same common nongenetically
determined diseases.
(C) Purebred dogs tend to have shorter natural life
spans than do nonpurebred dogs.
(D) The purchase price of nonpurebred dogs tends
to be lower than the purchase price of
purebred dogs.
(E) A dog that does not have genetically
determined abnormalities may nevertheless
have offspring with such abnormalities.
This is from the October 1993 test, Logical Reasoning section 1, question #12.
This is a weaken question. We start with the conclusion. The conclusion is "potential dog owners who want to reduce the risk of incurring costly medical bills for their pets would be well advised to choose nonpurebred dogs."
What is the evidence? As stated by posts above it is the fact that pure-bred dogs have genetic abnormalities and these are costly to fix. Non pure-bred dogs rarely suffer from the genetic abnormalities.
So we are looking to weaken this argument. We want a reason why these premises do not necessarily lead to this conclusion.
The logic has a flaw in it. We need to find that flaw. Answer Choice A is that flaw. Why? Because the one question we have not asked is, "Do the genetically determined abnormalities need to be fixed?" If the answer is "no" if we do not need to fix these abnormalities - if they are like a drooping tail or something that is not vital then people can feel free to get a purebred dog since they will not have to pay to get these things fixed.
So the answer is A.
Choice E is not correct because it requires too many assumptions. We have to assume that people are going to have offspring from their non pure-bred dogs and then, what need medical care for these offspring - maybe? This is too far away from the argument. Too many steps in between. A is much closer does not need so many assumptions on our part. Go with A.