The correct answers are:
- is nonrenewable;
The reserves of the coal are limited, and already, lots of coal mines have been emptied around the world, so it is a nonrenewable energy source which reserves will end up in the close future with this tempo of its usage.
- releases carbon dioxide when burned;
The coal is a natural storage for carbon dioxide, so when burned it releases huge amounts of carbon dioxide into the atmosphere, contributing to the ''Greenhouse Effect''.
- forms from organic remains;
This natural resources is formed on the basis of organic matter, namely from prehistoric types of trees that are long extinct. Since most of the coal originates from certain period of geologic time, one of the geologic periods is actually named after it, the Carboniferous.
