Answer:

1. Alternative resources for commonly used nonrenewable energy sources include wind, solar, hydro, geothermal, and biomass energy. These sources are renewable and have a lower environmental impact than nonrenewable sources.

2. Metals are used because they have unique properties such as high strength, durability, and conductivity which cannot be easily replicated by other materials. Additionally, metals are often essential for various industries and technologies.

3. Fossil fuels are hydrocarbons that are formed from the remains of dead plants and animals over millions of years. They are considered nonrenewable because they take millions of years to form and cannot be replenished in a short period of time.

4. Coal, crude oil, and natural gas are considered nonrenewable because they are formed from the remains of dead plants and animals that were buried underground and subjected to high pressure and temperature over millions of years. These resources take millions of years to form and cannot be replenished in a short period of time.