Of the countries that were the world's twenty

[BTGmoderatorDC]

Of the countries that were the world's twenty largest exporters in 1953, four had the same share of total world exports in 1984 as in 1953. Theses countries can therefore serve as models for those countries that wish to keep their share of the global export trade stable over the years.

Which of the following, if true, casts the most serious doubt on the suitability of those four countries as models in the sense described?

(a) Many countries wish to increase their share of world export trade, not just keep it stable.
(b) Many countries are less concerned with exports alone than with he balance between exports and imports.
(c) With respect to the mix of products each exports, the four countries are very different from each other.
(d) Of the four countries, two had a much larger, and two had a much smaller, share of total world exports in 1970 than in 1984.
(e) The exports of the four countries range from 15 percent to 75 percent of the total national output.

I'm quite confuse here, why Option C isn't the correct option?

OA D

[EconomistGMATTutor]

The conclusion: These countries can serve as models for those countries that wish to keep their share of the global export trade stable over the years.

The evidence: These countries had the same share of total world exports in 1984 as in 1953.

This question asks you to weaken the conclusion. There's a big ripe assumption being made here: Having the same share in those two years means that the shares remained stable between those two years. They could have fluctuated all over the place. Choice D shows us that indeed the shares for all four countries did fluctuate. The shares were much different in 1970. So much for stability.

Choice C makes an irrelevant comparison, a favorite wrong choice of the test authors. How the four compare to each other doesn't matter.

I'm available if you'd like any follow up.