A classic I saw from a Radio Nav paper :
Which of the following affects the maximum range of a radar?
a. Frequency
b. Wavelength
c. PRP
d. Pulse length
Of course all of these can, it depends which factor is limiting. The answer is probably PRP, as this detemines th maximum unambiguous range (this is not specified in the question).
This illustrates both the reason for multiple correct answers (or all incorrect) and the pure, unfair, deliberate nastiness of some of the question writers.
The question is only looking at the problem from one angle. The writer is either spectacularly ill-qualified to write radio navigation questions or has become so focussed on their interpretation of the question (and therefore the "right" answer) that they fail to see that as the question is written there are other posible answers. They have forgotten all their other knowledge while concentrating on maximum unambiguous range in this case.
Part of the problem and the focus is on tripping the candidate. Pulse length determines minimum range, so is a good wrong answer to offer if the examiner is trying to fool the candidate. The examiner forgets that with modern radars using pulse compression the pulse length can affect the required strength of the return signal and so, for a given power the maximum range at which a return can be detected.
Note that the effects of frequency/wavelength on attenuation and the influence of pulse compression on power recovery were taught in the course I attended, so all these answers fitted work I had learned towards this course.