Deforestation in Bihar has been caused by factors such as:

Agricultural expansion
Timber extraction
Fuelwood collection
All of the above

The correct answer is: d) All of the above

Deforestation in Bihar has been caused by a number of factors, including agricultural expansion, timber extraction, and fuelwood collection.

Agricultural expansion is the conversion of forests into agricultural land. This is often done to meet the growing demand for food and other agricultural products. However, it can have a devastating impact on forests, as it destroys the habitat of many plants and animals, and can lead to soil erosion and water pollution.

Timber extraction is the cutting down of trees for their wood. This is often done to meet the demand for timber for construction, furniture, and other products. However, it can also have a devastating impact on forests, as it removes large numbers of trees and can lead to the fragmentation of forests.

Fuelwood collection is the gathering of wood for use as fuel. This is often done by people who live in rural areas and do not have access to other sources of energy, such as electricity or gas. However, it can also have a devastating impact on forests, as it removes large numbers of trees and can lead to the fragmentation of forests.

All of these factors have contributed to the deforestation of Bihar. In recent years, the government of Bihar has taken some steps to address the problem of deforestation, such as planting trees and creating protected areas. However, more needs to be done to protect the forests of Bihar.