Inference questions ask you to draw a conclusion. You must select the answer choice that most directly follows the premises of the passage without needing any major new assumption.
The premise here is that once imports of goods were banned to protect industries who could make these products domestically, other industries ('export-dependent industries') which would buy these products had a harder time competing abroad. Essentially this means that these export-industries (who would be the buyers of the banned imports) were forced to incur additional cost as a result of the ban (meaning these products cost more when they are purchased domestically from the fledgling industries than when they are imported)
A is correct
To look at a detailed solution, please review
GMATPrep question 2003. You can find similar questions by searching for topic='Inference' and difficulty='400-500' in the
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Good luck,
-Patrick