I've seen several high-bypass engines where within the flat-rating range (say, ISA+15C and below), the TO thrust was held constant for increasing altitude. In other words, N1/EPR/temps etc. increased with altitude. This is a tradeoff by the manufacturer to meet certain customer requirements e.g. MEX-to-Europe.
On the other hand, if N1 etc. is not "bumped" at altitude, then thrust must decay as air density decreases.
So - to answer the quiz, you have to get inside the head of the guy who wrote the question, and assess how much you think he knew about the subject. My bet - the answer he expects is b).