Benzene is a colorless or light yellow liquid at room temperature and is a well-known environmental pollutant. It is widely present in the environment due to various natural and human-made sources..

1. Automobiles, especially those running on petrol, are a significant source of benzene pollution. Since benzene is a component of petroleum products, including motor fuels, its combustion in vehicle engines releases benzene into the air, contributing significantly to air pollution.

2. Tobacco smoke is a source of benzene exposure. Both active smoking and passive smoking introduce benzene into the body, as tobacco smoke contains benzene. Prolonged exposure to such smoke increases health risks.

3. Wood burning releases benzene and other pollutants like polycyclic aromatic hydrocarbons (PAHs) due to incomplete combustion. Hence, wood burning is a source of benzene pollution.

4. Varnished wooden furniture can be a source of benzene exposure but it is less direct and typically with lower exposure levels once the varnish has cured. Therefore, it is not considered a significant source of benzene pollution.

5. Polyurethane-based products do not contribute significantly to benzene pollution. They are more associated with volatile organic compounds (VOCs) and other chemicals rather than benzene itself.

Thus, the major contributors to benzene pollution are automobile emissions, tobacco smoke, and wood burning . Hence the correct answer is A. 1, 2 and 3 only.