Choice "C" is correct. An action for strict product liability does not require a showing of negligence. The product must have been unreasonably dangerous when it left the seller's hands.
Choice "a" is incorrect. In an action for strict liability in tort, High's contributory negligence would be irrelevant.
Choice "b" is incorrect. Custom in the industry is good evidence that there was no negligence, but a whole industry can be found to be following a negligent practice, and industry custom is not a defense in a strict liability product liability case.
Choice "d" is incorrect. The fact that the wholesaler did not have an opportunity to inspect is not a defense.