Final answer:
The legal defense against negligence that is not valid among the options provided is D. apparent authority. Apparent authority is related to agency law and does not offer a defense in negligence cases.
Step-by-step explanation:
The defense against negligence that is not legally valid among the provided options is D. apparent authority. The defenses such as an intervening cause, assumption of risk, and contributory negligence are legitimate defenses in a negligence lawsuit. An intervening cause is an unforeseen event that breaks the chain of causation and absolves the defendant of liability. Assumption of risk occurs when a plaintiff knowingly exposes themselves to danger and thus carries some responsibility for their injuries. Contributory negligence implies that the plaintiff may have contributed to their own harm through their negligence, potentially reducing or eliminating the defendant's liability.Apparent authority, on the other hand, refers to a situation where a person appears to have the authority to act for another entity but, in reality, lacks the actual authority. This concept is more pertinent to agency law and does not provide a defense against a charge of negligence. Therefore, D. apparent authority is not a valid legal defense in a negligence claim.