Strategy needed. Solving Hard RC problems easily but not Easy problems

Hi,

I am facing a peculiar problem regarding RCs.
I was very weak in RC and put my full efforts to conquer it. I read blogs, books and practiced so much that I started solving hardest questions without difficulty.
However, I am overthinking easy questions. For example:

A gmat problem which I cannot reproduce fully:
Paragraph:
Opponents of a certain animal breeding program suggest that zoos should focus their efforts on preserving endangered subspecies of a certain animal and thereby prevent the extinction of these subspecies. If zoos breeding that animal breed it as one species, the zoos could save resources and make these resources available to other endangered species of same family.

Question:
The author of the passage suggests that by breeding the animal as one species, zoos would be able to:
a. use the resources to preserve other species of same animal.
b....
c....
d. prevent the extinction of existing subspecies of the animal.
e...

Now I had to choose between a and d.

Easy question would prompt me to choose 'a' as it is simple and straight forward.
However, on careful observation, it is saying 'other species' and not 'other extinct species'. So as the overall picture tells me that opponents are saying that zoos can prevent the extinction and I chose 'd' which turned out to be wrong!

Source: This is from the extra questions I bought from GMAC .

Did I over-analyze it? or was there any mistake on my part?


Please help me resolve this peculiar problem.

Thanks a lot.
Karthik