Q: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Question: What measure defines the frequency of lung cancer among people who smoke 20 cigarettes a day compared to those who do not smoke ?:
Options: <1> Accumulated incidence. <2> Incidence density. <3> Relative risk. <4> Attributable risk. <5> Etiological risk fraction.
A:
3