Residents of three villages with three different types of water supply were asked to participate in a study to identify individuals who were cholera carriers. because there had been several recent deaths due to cholera, almost everyone participated in the study and underwent examination and testing. the proportion of residents in each village who were carriers was computed and compared. what is the proper classification for this study?
a. cross-sectional studyb. case-control studyc. prospective cohort studyd. retrospective cohort studye. experimental study