thanks for the comments. I agree that the question is quite bad. I think that the intention of the examinors was the following:
When there is a changing magnetic flux through a conducting loop, an emf is induced and in this case a current as well. The current has an associated magnetic field which must oppose the change in the magnetic flux. If it didn't, it would contribute to the change in magnetic flux and subsequently create a greater induced current. This would violate the law of conservation of energy.
John D. is right in writing "One of the standard tricks for gaming the test uses the "principle" stated by Sherlock Holmes: when you have eliminated the impossible, whatever
remains, however improbable, must be the truth." I hope that questions in fortcoming exams will be of higher standard.
Regards,
Antti
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