What plays the most important role in causing or promoting cancer,according to the World Health Organization? 

A)  cigarette smoke 
B)  genetic factors 
C)  viruses 
D)  environmental pollutants

The World Health Organization (WHO) recognizes that several factors play a role in causing or promoting cancer, including genetic factors, viruses, and environmental pollutants. However, according to the WHO, the most important factor in causing or promoting cancer is cigarette smoke. Tobacco smoke contains more than 70 chemicals that are known to cause cancer, and it is estimated that smoking is responsible for around 22% of all cancer deaths globally. Therefore, the best choice based on the WHO's perspective would be A) cigarette smoke.