Which of These Observations Provides Unequivocal Evidence of the Formation

Which of these observations provides unequivocal evidence of the formation of a nonclassical ion in the following reaction?

A) retention of exo-stereochemistry in the product ester
B) racemization of the product in the reaction
C) faster reaction for the exo tosylate than the endo-tosylate
D) None of these give unequivocal evidence of a nonclassical cation.
E) a and b both give unequivolcal evidence for a nonclassical cation.