Icelandair, an airline company, has realized that some customers don't have email or don't read it regularly. They decide to restrict the mailing to customers who have recently registered for a "Win a Trip to Reykjavik, Iceland" contest, figuring that those with Internet access are more likely to read and respond to their email. What is the sampling frame? All frequent flier customers of the airline All international fliers Customers who have recently registered for the "Win a Trip to Reykjavik, Iceland" contest Fliers in Europe None of the options apply