ANSWER: C
C is the correct answer because there is not enough research to determine whether MS is caused by genetics, environmental factors, or a exposure to pathogens. It is also manifested differently across the world; therefore there is no conclusion as to why MS occurs. A is not the most true because there are multiple tests that need to be done in order to positively diagnose MS. Check the Diagnostic Test page for more details. B is not the most true because neurons do not have to be fully demyelinated for a patient to have MS, partial demyelination or presence of scar tissue can indicate MS. Varying levels of demyelination allows for the varying presentations in patients. D is the not most true because every patient with MS presents differently! Ataxia is a common clinical manifestation but is not present in every patient.