Which of the following is an example of a panel survey?
1.a survey of 1,000 high school seniors that is repeated with a new group of seniors every year for ten years
2.a onetime survey of 25 percent of each of the four grades in a particular high school
3.a study of 1,000 high school seniors who are then contacted every two years for a ten-year period to participate in a follow-up survey
4.a survey of 1,000 high school seniors conducted by a panel of sociologists with different specialties