What type of materials are most susceptible to mold infestation?

The correct choice highlights materials that are organic in nature and provide an ideal environment for mold growth. Wood, paper, and insulation are all materials with high cellulose content, which is a food source for mold spores. These materials can retain moisture, especially in environments that are humid or where water leaks occur, creating the perfect conditions for mold to thrive.

Wood, being organic, can absorb moisture from the air and from the ground, making it susceptible to mold if not properly treated or maintained. Paper also offers a rich source of nutrients for mold due to its fiber composition. Similarly, insulation may be made from materials that can trap moisture and provide a dark, damp environment conducive to mold growth.

In contrast, materials like concrete and steel are less prone to mold because they are inorganic and do not provide food sources for mold. Glass and metal are also non-porous and do not easily absorb moisture, making them less likely to support mold growth. Plastic and rubber can resist moisture to some extent, but they do not have the organic compounds necessary for mold to thrive, and thus they are not as susceptible as the organic materials mentioned.