Smoking reduces a person's life span by an average of
a. 1 to 2 years
b. 4 to 5 years
c. 10 to 11 years
d. 13 to 14 years

Smoking reduces a person's lifespan by an average of 13 to 14 years.

Explanation: 

People who smoke take a minimum of 13 years off their expectancy, a brand new study has found. On the opposite hand, those that kick the habit before age forty scale back the surplus risk of death related to continued smoking by around 90 percent, in step with the study in Thursday's New England Journal of medication.