Which of the following is an example of a census?
a. Weigh every child at an elementary school for a study of physical fitness at the school.
b. Survey parents whose children attend a local elementary school by randomly selecting 50 parents from the school’s records.
c. The U.S. Population Census
d. Poll students at a college by including a pop-up window in the online registration form. Students have to answer the survey questions before they can register. Try to catch the remaining students at the admissions window when they register in person.