Which of the Following Refers to the State-Of-The-Art Defense

Which of the following refers to the state-of-the-art defense?

A) The defendant proves that a warning on the product would not have helped.
B) The defendant proves that there was insufficient scientific knowledge to make a safer product at the time it was manufactured.
C) The defendant proves that the plaintiff had insufficient knowledge to purchase the product.
D) The defendant proves that the warning could have been understood by any reasonable person.