What is a type of fungus that affects plants or grows on inanimate objects?

The correct answer is mildew, a type of fungus that typically affects plants as well as surfaces in moist environments. Mildew can appear as a thin, often powdery layer that thrives in humid conditions, commonly found on plants, textiles, and surfaces that retain moisture.

While mold is also a type of fungus, it typically refers to various organisms that can grow on both living and non-living surfaces, but specifically indicates a different morphology compared to mildew. Yeast is another kind of fungus that primarily ferments sugars and does not grow in the same way as mildew or mold on surfaces. The broader term fungi encompasses all three forms—mildew, mold, and yeast—yet does not specifically indicate the type of growth affecting inanimate objects or plants. Thus, mildew is the most accurate choice in this context.