Which of the following is NOT an example of opening protection?

Windowless doors are not considered an example of opening protection because opening protection specifically refers to measures taken to safeguard openings in a structure—like windows and doors—against wind and debris during storms, particularly hurricanes. Impact-resistant windows and skylights, as well as hurricane shutters, are all designed to withstand high winds and flying debris, which is vital in hurricane-prone areas where such openings are more vulnerable. By eliminating the window in a door, windowless doors eliminate an opening, but they do not contribute to protection in the same proactive way that impact-resistant materials or barriers do. Therefore, they do not function as protective elements against storm damage, making them distinct from the other options listed.