(B) is correct.

Issue: What is the best defense to a strict liability claim?

Rule: One who sells any product in a defective condition unreasonably dangerous to the consumer or to his property is subject to liability for physical harm thereby caused to anyone whose injury was foreseeable, including the ultimate consumer, or to his property, if (1) the manufacturer or supplier is engaged in the business of selling the product in question; (note that a commercial  supplier has a duty to supply a safe product); (2) the product is unreasonably dangerous to the consumer or to his property (in which case the duty to supply a safe product is breached); (3) the defect existed while in the  hands  of  the  manufacturer  (meaning  the  product  was  not  altered  after  it  left  the  hands  of  the  manufacturer); and (4) there is actual harm to the person or property.  Pure economic loss – i.e., the value of the defective product itself –cannot be recovered. Privity is not a requirement under strict liability. Defenses to a claim of strict liability include, inter alia,  assumption of risk, which is when the plaintiff  continues  to  use  the  product  unreasonably  even  after  he  learns  about  the  risk  and  the  failure to heed the warning accompanying the product.

Analysis: Here,  the  manufacturer  issued  a  warning  for  the  swing  set  and  thus  protected  itself  against  a strict  liability  claim  for  exactly  the  activity  that  the  manufacturer  warned  against. By failing to heed the warning, the parents and child can be said to have assumed the risk of using the swing set. Thus, (B) is the correct answer.

(B) is correct because it is the best defense to a strict liability claim.

(A) is incorrect because strict liability extends to beyond just the purchasers of the product. The manufacturer may be liable to anyone whose injury was foreseeable.

(C) is incorrect because while modification of the product may be a defense to strict liability, here, (B) is the better answer given that the manufacturer warned against the exact activity that caused the child’s injury.

(D) is incorrect because the “last clear chance” theory is not applicable to strict liability actions.