long time since I was involved in ATPL exams, but applying the terminology used in the real world, when instructing I would say, for example, "increase your nose-down pitch attitude to maintain a constant mach number". Likewise, "decrease your nose-down pitch attitude to reduce speed".
Another way of thinking about it, look at the markings on the artificial horizon - they don't have a minus number for nose down -they simply increase away from zero degrees in both directions, nose up and nose down.
So, my answer to the question using this logic would be:
a.) increase.
Unfortunately however, who can ever be 100% sure that the powers that be are using the same logic?
