Вопрос по английскому языку:

Помогите пожалуйста
Объясните почему здесь расставлены такие артикли:
1.This is the resource. The resource is important.2. This is the manager. The manager is American.3. This is a plant. The plant produces these goods.4. This is fuel. Fuel is good.5. These are services. The services are important for plants.6. These are books. The books are on agriculture.7. These are managers. The managers are Russian and American.8. These are goods. The goods are industrial.9. These are people. The people are from small towns.