Answer: option (B). knowledgeable user.
Explanation: knowledgeable user simply means If a particular danger is or should be commonly known by particular users of the product, the manufacturer need not warn those particular users. An example is a case of Stan, an air-conditioning and heating technician, files a suit against Temp-Set Corporation, alleging that its thermostats are unreasonably dangerous due to the possibility of electrical shock, Temp-Sets defense is knowledgeable user.