You will be given a definition of a task first, then some input of the task.
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: In a cohort study, the number of new cases of disease per person per unit of time is: 
 Options:  <1> The annual incidence. <2> The cumulative incidence or probability. <3> The prevalence rate <4> The density or incidence rate. <5> The relative risk of developing the disease.
Output:
4