Today there are many fires than in the past. Over 100,000 wildfires burn each year in America. Russia has 20,000 to 35,000 wildfires every year. Australia has on average 60,000 each year. These fires destroy（损害）huge areas of forests and burn hundreds of homes.
Many experts believe there are several reasons for this sudden increase in fires. The first reason is climate（气候）change. Recent weather has been warmer and drier. This leads to dangerous fire conditions. When lightening strikes（发生雷电），dry grass easily catches fire. Hot winds add to the problem. The wind spreads a fire quickly. In 2010, Russia had the hottest and driest summer in a century. In just one month, 500 fires destroyed over 2,000 homes. Some people lost their lives.
Traditional fire-fighting practices are another reason for the increase in fires. In America, firefighters used to quickly put out every fire. They didn’t allow the grass and trees to burn. As a result, today many forests have thicker vegetation（植被）.Thicker vegetation means more fuel（燃料）for fires. Also, without fires from time to time, forests become overcrowded and unhealthy. Some trees are dead. The dead wood then easily catches fire. So surprisingly, America has many more fires today partly because of its past fire-fighting practices.
Scientists now understand that a fire can be a natural part of a healthy forest. As a result, countries like Australia allow more fires to burn naturally. Sometimes, fire fighters even start fires to get rid of（去除）dead wood. Of course, they carefully control the fires. The fire thins out old trees. This allows sunlight to reach the ground. As a result, fires help new trees to grow. Therefore, if a fire is not a serious threat（威胁）to people, firefighters may let it burn naturally.
Why did Russia have so many fires in one month in 2010?

A．Because lightening spread the fire.

B．Because there was much fuel for fires.

C．Because there were not enough firefighters.

D．Because it was unusually hot, dry and windy.

What is the main idea of Paragraph 4?

A．Fires are serious threats to human beings.

B．Australian firefighters don’t put out fires.

C．Fires can play an important role I forests.

D．It’s difficult for firefighters to control the fires.

Which of the following is true according to the passage?
A. Not all the fires in the forests must be put out.
B. People’s carelessness leads to dangerous fires.
C. Australia allows all the fires to burn naturally.
D. There are more fires in Russia than in the USA.