CR: GMAT Paper set 18

[Samy]

In response to viral infection, the immune systems of mice typically produce antibodies
that destroy the virus by binding to proteins on its surface. Mice infected with a
herpesvirus generally develop keratitis, a degenerative disease affecting part of the eye.
Since proteins on the surface of cells in this part of the eye closely resemble those on the
herpesvirus surface, scientists hypothesize that these cases of keratitis are caused by
antibodies to herpesvirus

Which of the following, if true, gives the greatest additional support to the scientists’
hypothesis?

A. Other types of virus have surface proteins that closely resemble proteins found in
various organs of mice.
B. There are mice that are unable to form antibodies in response to herpes infections,
and these mice contract herpes at roughly the same rate as other mice.
C. Mice that are infected with a herpesvirus but do not develop keratitis produce as
many antibodies as infected mice that do develop keratitis.
D. There are mice that are unable to form antibodies in response to herpes infections,
and these mice survive these infections without ever developing keratitis.
E. Mice that have never been infected with a herpesvirus can sometimes develop
keratitis.

Dan, I am trying this as per your approach.

Fact: Immune systems of mice destroy virus with the help of antibodies that bind on protein.
P1: Mice with H develop K.
P2: Proteins in eye resemble those on H.

scientists hypothesize that these cases of keratitis are caused by
antibodies to herpesvirus: This can only be true if antibodies bind on the protein that the eye has and not on the protein of H.

Choice D shows the reverse condition and it confirms my Guess. So it should be right.

Please can you add or tweak this approach.

[dbernst]

Samy,

That looks great to me! My only additional suggestion would be to create a weaken/strengthen slash chart in order to keep track of each individual answer choice as you work through your process of elimination. Mine looks like this:

A. Other types of virus have surface proteins that closely resemble proteins found in
various organs of mice.
-Irrelevant: we don't care about other types of viruses.
B. There are mice that are unable to form antibodies in response to herpes infections,
and these mice contract herpes at roughly the same rate as other mice.
-Irrelevant: we are not concerned with rates of herpes infection
C. Mice that are infected with a herpesvirus but do not develop keratitis produce as
many antibodies as infected mice that do develop keratitis.
-Weaken: this indicates that perhaps teh antibodies are not causing the keratitis
D. There are mice that are unable to form antibodies in response to herpes infections,
and these mice survive these infections without ever developing keratitis.
-Strengthen: A lack of antibodies -> a lack of keratitis; this supports the contention that antibodies are involved in the development of keratitis
E. Mice that have never been infected with a herpesvirus can sometimes develop
keratitis.
-Irrelevant, but Attractive Distractor: The text only refers to these specific cases of ketatitis; it never suggests that all cases of keratitis are caused by antibodies.

Of course you won't do all of this writing on your Official GMAT, but just jotting down S, W, or NA can really help your process of elimination on weaken/strengthen questions.

-dan

[Samy]

Thanks..
Thats at a Record Speed.
Amazing within 30 mins I have an Ans.
I have a week left for D-Day.
Any suggestions will really help.

[jigar24]

dbernst: Thanks for the explanation. I have a further doubt regarding C -

Isn't this an assumption - as it's not certain that all the antibodies developed in mice with H virus is misdirected causing K. So of all mice with H some may be misdirected to cause K but others may rightly be directed to overcome H. In either cases all infected mice produce the same # of antibodies.

I can't think clearly how this statement weakens. Could you please correct my thinking.

Thanks.

[RonPurewal]

Consider smoking vs. lung cancer.

Choice C is like saying "People who didn't develop lung cancer smoked just as many cigarettes as did those who did develop lung cancer."
--> If this were true, it would definitely go against the idea that smoking causes lung cancer.

Cigarettes -- Antibodies
Lung cancer -- Keratitis

Same deal.