Fact 1: Smoking causes direct damage to the lungs. Fact 2: Many people smoke cigarettes. Given the two facts above, what causes direct damage to the lungs?
Choose from:
[1]. cigarettes.
[2]. burning.
[3]. tissue.
[4]. hypothyroidism.
[5]. breathing.
[6]. hydrogen.
[7]. amoebae.
[8]. influenza.
[1].