A、Tractors and hand tools. B、Helicopters and airplanes. C、The slightly higher humidity. D、The 20-kilometer fire lines. C

The largest fire has burned about 500 square kilometers of the Angeles National Forest, north of Los Angeles. Some 3 600 firefighters are attacking the flames in steep terrain, using bulldozers, tractors and hand tools. They are also setting backfires to clear away dry brush, and using helicopters and airplanes to drop water and fire retardant. They got some help on Tuesday from slightly higher humidity as they worked to protect homes in hillside communities. Officials say they have carved out nearly 20 kilometers of fire lines to slow the advance of the flames.
Firefighters are working to protect communication and scientific facilities on Mount Wilson, which overlooks downtown Los Angeles. The site is home to transmitters for most of the city’s television stations, as well as some radio stations, several mobile phone companies and police communication systems.
1.  What is this news report mainly about?
2.  What helped the firefighters as they worked?