Psychologist timothy brown has studied generalized anxiety disorder and social anxiety disorder extensively. he found through his research, and subsequently argued, that generalized anxiety disorder and social phobia are manifestations of which factor on the big five theory of personality?

The answer is "Neuroticism".

Neuroticism is one of the 'Big Five' factors in the investigation of identity in psychology. It is estimated on a continuum, going from passionate dependability (low neuroticism) to enthusiastic insecurity (high neuroticism). 
A neurotic identity is described by industrious, frequently unbalanced, stressing and nervousness. A man may endeavor to be a stickler amid their regular exercises, and experience worry because of occasions that are outside their ability to control.

Ithink it would be choices a and b. hope this !