VI. Fill each blank with one suitable word.

The greatest enemy of forests is fire. Every year millions of acres of forests are …1… by forest fires. Most of these fires are started …2… man. More forest fires can be traced to campers, and smokers …3… to any other …4…

Some of the people who start forest fires do …5… because …6… ignorance. They do not …7… to know that …8… is important to watch a camp fire …9… and to put the fire …10… with water when they leave. It is …11… important to know that camp fire should be built only in safe …12…, and that forest soil will often burn because it is so …13… of plant materials. In …14… weather, such soil may …15… ablaze by a camp fire.