Indoor air pollution can arise from both natural processes and human activities. which of the following is a combination of three natural causes of indoor air pollution? a) secondhand smoke, mold, and radon gas b) radon gas, pesticides, and dust mites c) asbestos, mold, and radon gas d) volatile organics, sulfur dioxide, and formaldehyde

C) asbestos, mold, and radon gas

This three options are a natural cause ofIndoor air pollution.
Radon is a radioactive gas that comes from the break down of uranium.
Asbestos is a set of six naturally occurring silicate minerals. Both asbestos and radon can be found in materials used in home construction like paints, building materials, ceiling and floor tiles.
Molds are microorganisms that can easily grow when there is high humidity, making it another natural cause.

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Very hard to understand