Barotrauma - ok it’s when trapped gas can't escape, causing pain.

So,....firstly the question asks about the middle ear - no sinus there so can't be b) even though as a statement on its own it is true, that's the gotcha.

a) less likely as barotrauma most severe in ears on descent due to increasing rate of increase in pressure.

c) it can happen but it’s not the highest on the list and isn't expected so that leaves

d) barotrauma most likely in descent for reasons stated above and the implication of the respiratory infection is that they have a cold so blocked eustachian tube etc...