In modern schools, teachers play the key role ___________ a guide for students to prepare themselves for lifelong learning.

I. Read the passage. Circle the best answer A, B, or C to each of the questions.

There are many reasons for reducing the forest areas, and this causes many complicated problems for any nation without any exception. Due to the population explosion, many governments need more land for residents to live and develop the economy. They also clear forests to build dams for generating electricity or to develop resorts and recreational complexes. Besides, a huge number of trees are logged illegally to trade wood. All of these lead to serious issues as forests always have an important role in the ecosystem balance. It is undoubted that when a forest area is destroyed, the following results affect the other neighbor regions. The first negative effect of the loss of forest lands is flooding. Forests help to prevent erosion and flooding and without them, the downstream areas tend to be inundated frequently in rainy and hurricane seasons. Another problem is global warming. Forests are often considered as the lungs of the earth because they absorb the carbon dioxide and release the oxygen. This helps to refresh the atmosphere and lower the rate of the carbon dioxide in the air. If not, the average temperature will be higher and higher since the emission of the gas into the atmosphere increases every day. Consequently, the price we would pay for the flooding or for the increase of greenhouse gases is not only the damaged and polluted environment but also our deteriorated health and lives. To save ourselves, it is advisable to join hands in protecting and growing more and more forests.

What is the passage mainly about?