In a polling organization's survey, 2,445 undergraduates who attend a university and live in the United States are asked whether or not they had spent more than $200 on food in the last month. Identify the population and sample:
a) Population: Students who spent more than $200 on food, Sample: 2,445
b) Population: All undergraduates in the United States, Sample: Survey
c) Population: Students surveyed, Sample: 2,445
d) Population: Students attending a university, Sample: 2,445