Fact 1: Lung cancer is most often caused by exposure to tobacco smoke. Fact 2: Tobacco smoke consists of solid particles and gases. Given the two facts above, what is most often caused by exposure to solid particles and gases?

Possible answers: (1). syphilis (2). diabetes (3). contamination (4). scattered light (5). lung cancer (6). hair color (7). global warming (8). Pollution
The answer is:
(5).