how would you answer the following??

In January, 2001 forty heterosexual hemophiliac patients (all males) were asked to participate in a 3 year prospective study . The men were to undergo an interview, physical examination, and blood testing for HIV status every 6 months for 3 years. Among the 40 subjects there were 30 who were seronegative and healthy for the entire duration of the study, and all of these were followed for the entire 3 years. During the initial screening, 2 of the men were found to already be HIV+, although none of them had clinical signs of AIDS. The table below describes the 10 subjects who either tested HIV positive, or became lost to follow-up, or already were HIV positive at the start of the study.

Legend:

HIV+= found to be HIV+ at the very beginning of the interval observation period

?= lost to follow-up

************* Follow-up **********************Subject#InitialScreeningJan. 2001June 2001Jan. 2002June 2002Jan. 2003June 20031---------------------------------------------HIV+--2---------------------------------------------?3------------------HIV+-----------------------------4---------?5---------------------------?6---------------------------------------------?7---------HIV+--------------------------------------8---------------------------------------------?9HIV+------------------------------------------------------10HIV+---------------------------------------------?

What was thecumulative incidenceof seropositivity (HIV+) during the 3 year study?

a.5/40

b.3/10

c.5/35

d.3/38