When Elliot engages in intense exercise, particularly in cold weather or during allergy season, his bronchial tubes fill with mucus and contract. This causes him to cough and have serious breathing difficulties. Elliot has

The term for gene variants that can arise before or after birth, or be inherited from parents, is ________

a. epigenetics. b. mutation. c. RNA manipulation. d. DNA distortion.

In recent years, the number of teenagers who start smoking each year has ________

a. increased dramatically b. slightly decreased c. dramatically decreased d. hardly changed