I think people are getting confused here about the basic meaning of the sentence:
Eliminating B and D on the basis of tense. Has not/ had been/had been
We are left with A, C, E
Check A first:
if one can't understand the meaning, test the timeline:
Past perfect----->Past------>Present
He had not experienced any symptoms till adulthood (From birth till adulthood)----->He was facing facial paralysis (which according to passage suggests is a symptom of GBS and not complications of Polio)----->Diagonis may be wrong (suggestion in present)
C's timeline
Early on he experienced problems and having not experienced...hhmmmmmmm....
----> He had facial paralysis and also did not have any symptoms (Overlap of timeline....because past and present perfect continuous suggests continuation till present) -- > Total confusion here!
E's timeline
He did not face symptoms but had facial paralysis
Its like the best contradiction ever!
How can a person not face any symptom but have facial paralysis?
E negated.
Left with A
So OA is A
Hope this helps!