IanStewart
Some of the posts above seem not to capture the logic of the question. The only relevant fact is this: if someone joined the International Business program after 1994, they took Applied Economics. So (taking the contrapositive) if someone didn't take Applied Economics, they didn't join the International Business program after 1994. So the answer is C (though C needs to say 'prior to 1995', and not 'prior to 1994' to be perfectly correct).
All of the detail about Microeconomics is simply irrelevant. It is certainly possible that some International Business students took Microeconomics prior to 1990, which is why E is wrong.
Can you explain that it's also possible that a student took applied economics prior to 1995 considering the same logic you used(after 1994, if all students took app. econ. then it's possible that one of the students took applied economy prior to 1995). In this case, those answers would be equally true, isn't it?