it's about north american PHD program, and DOES NOT WEAKEN problem.I can see why B is correct, because age of applicants has little to do with the decline, but I am also not sure about E, which states applicants outside north America has declined.
It's a causal argument.The mystery is that there has been a decline in the number of applicants for admission to PHD art history programs. The author concludes that the cause must be less interest among recent North American college students in choosing an art history career.Each of the wrong answers weakens by giving an alternative cause. Choice A suggests that the decline is actually due to a lack of reporting. Choice C suggests that the decline is due to data error. Choice D suggests that the decline could be due to the students simply beginning their art history careers without a PhD. Likewise, choice E suggests that the reason for the decline is due to a drop in the interest among non-North Americans (notice that the conclusion specifically blames North American college graduates.)