Which sample is biased?
1) interviews of random teenagers who attended a rock concert to find out which musician teens enjoy most
2) a poll randomly surveying half of the students in grade 7 to find out which seventh-grade teacher at the school is most liked
3) an online survey by a game development company taken after the game closes to find out which features of a new game players liked the most
4) a questionnaire delivered to two employees from every department of an office to find out whether employees like the new coffee machine
