Final answer:
In a design defect case, the plaintiff must prove that the product was defective and that there was a safer and available alternative design that the manufacturer did not use. Proof of harm caused by the failure to use a safer design is also essential, but not the notion that the product was defective without alternatives.
Step-by-step explanation:
To succeed in a design defect case, a plaintiff must prove two key elements which are:
The product was defective even if there was no reasonable alternative design.
An alternative design was safer and available and the manufacturer did not use the alternative, thereby implicating option D.
Option B, which suggests that the failure to use a safer design must be the cause of harm to the plaintiff, is also important in establishing causation in a design defect case. However, option A as phrased is not traditionally a requirement for a design defect claim since a viable alternative design is usually necessary to show that the original design was defective. Option C addresses failure to warn, which is typically a separate claim from a design defect.
In context, a situation such as described where brake failures in automobile models were known before sale can illustrate a manufacturer's liability in terms of foreseeability and knowledge of the risk, strengthening the claim that a safety engineering decision was poor due to adequate testing information indicating a potential harm, but was ignored.
In the event of an injury, the manufacturer could be held liable for the design defect, particularly if there were a feasible and safer alternative design that was not implemented.