an example of heating something is heating a building & a source of heat can be used to heat something ->  a source of heat can be used to heat a building  a source of heat can be used to heat a building & natural gas is a source of heat by burning ->  natural gas is used for heating building by burning  natural gas is used for heating building by burning & a home is a kind of building ->  natural gas is used for heating homes by burning  fossil fuels are a nonrenewable resource & natural gas is a kind of fossil fuel ->  natural gas is a nonrenewable resource  natural gas is used for heating homes by burning & natural gas is a nonrenewable resource -> natural gas is a nonrenewable resource that is used for heating homes