Type I buildings typically use reinforced concrete and ________ in their construction.

Type I buildings are classified as non-combustible, which means they are constructed using materials that do not ignite or support combustion. The use of reinforced concrete and protected steel-frame in these buildings contributes significantly to their structural integrity and fire resistance.

The inclusion of a protected steel frame means that the steel is treated with protective materials or coatings that can resist high temperatures, thus maintaining its structural strength during a fire. This enhances the overall safety of the structure since steel that can withstand extreme heat is less likely to deform or fail in the event of a fire.

Other construction methods, such as treated wood-frame or unprotected concrete frame, do not provide the same level of fire resistance or structural support under fire conditions. Lightweight aluminum-frame, while strong, is not a standard material associated with Type I construction and is typically not used in high-rise or fire-resistive buildings due to its lower melting point and susceptibility to heat. Therefore, the choice of protected steel-frame complements the non-combustible nature of Type I buildings, making it the correct answer.