In a 2011 study, Wilkinson, Sebanz, Mandi, and Huber observed the reactions of 7 tortoises when exposed to an eighth tortoise that had been trained to yawn on command. Researchers were specifically...

In a 2011 study, Wilkinson, Sebanz, Mandi, and Huber observed the reactions of 7 tortoises when exposed to an eighth tortoise that had been trained to yawn on command.  Researchers were specifically looking to see if the 7 observed tortoises would yawn in reaction.  What is the population of this study?

1. All tortoises

2. Zookeepers

3.The 7 tortoises in the study

4.Tortoises that yawn when another tortoise yawns