Cabin crew members are trained to respond to medical emergencies, including situations involving unconscious passengers. They are indeed allowed to assess the condition of an unconscious passenger, which includes checking their vital signs like pulse and breathing.
The phrasing in the chosen answer suggests that cabin crew can take a pulse, except in cases where the individual is unconscious—this would be a misunderstanding. If a passenger is unconscious, checking their pulse is precisely what is needed to evaluate their medical state. Thus, cabin crew can and should assess vital signs regardless of the passenger's consciousness, as it allows them to provide appropriate emergency response or inform medical personnel when necessary.
In contrast, looking at the other options, the first one suggests an unconditional allowance that doesn't consider the context of their duty limitations or protocols. The second option states a complete prohibition that misunderstands the cabin crew's emergency role, whereas the last suggests that actions depend on specific conditions, which is less precise than the direct responsibility of crew members to assess and respond to emergencies effectively.