The eighth-grade students at Shady Oak School took a poll about their afterschool activities. The study concluded that 75% of the eighth-grade students at the school currently take part in at least two afterschool activities, which is not a valid generalization. Which sample could have led the researcher to make the invalid generalization?
every other eighth-grade student who was issued a report card during the fall semester
an equal number of eighth-grade boys and girls picked randomly from the school directory
an equal number of eighth-grade students chosen by chance from the athletic teams and school clubs
every third student who enters any eighth-grade class at a particular hour of the day