Residents of three villages with three different types of water supply were asked to participate in a study to identify cholera carriers. Because several cholera deaths had occurred in the recent past, virtually everyone present at the time submittd to examination. the proportion of residents in each village who were carriers was computed and co,pared. This study is a
a. Cross sectional study
b.Case -control study
c. Concurrent cohort study
d. Non -concurrent
ans:a. Cross sectional study