Answer: Choice 3.
The number of people purchasing coffee each day in a coffee shop
Reason:
It's not possible to have a decimal or fractional amount of people. So we select the value from the set {0,1,2,3,4,...}
On the other hand, it is possible to have a decimal temperature like 98.6 degrees, which means we rule out choice 1. Choices 2, 4, and 5 are a similar story.