Which material is particularly vulnerable to fire, moisture, and insect damage?

Wood is particularly vulnerable to fire, moisture, and insect damage due to its organic nature. Being a natural material, wood can easily ignite in the presence of flames, making it highly flammable. Once exposed to moisture, wood can also warp, rot, or develop mold, compromising its structural integrity and appearance. Additionally, wood is an attractive habitat for various insects, such as termites, which can cause significant damage by tunneling through it and weakening its structure.

In contrast, materials like concrete and masonry are generally fire-resistant and stable in moisture conditions, while steel, although it can be affected by fire in terms of structural performance at high temperatures, does not suffer from moisture or insect damage in the same way wood does. Thus, the susceptibility of wood to these hazards makes it the correct answer in this context.