Final answer:
Option (B), The protein that gives skin its strength by providing tensile strength to the connective tissues is collagen.
Step-by-step explanation:
The protein substance of complex fibers that gives skin its strength is collagen. Collagen fibers are an essential component in the connective tissues of the dermis layer of the skin, where they provide tensile strength and prevent the skin from being torn or separated from surrounding tissues.
Besides collagen, other proteins like elastin provide elasticity, allowing the skin to stretch and return to its original shape, while keratin is another protein that contributes to the protective properties of the skin. In contrast, melanin is the protein that gives skin its color.