Final answer:
According to Newton's 1st Law of Motion, an object at rest will stay at rest unless acted upon by an external force. In this case, the water bottle remains where it was left because no external forces acted on it.
Step-by-step explanation:
Newtons's 1st Law of Motion: An object at rest will stay at rest, and an object in motion will stay in motion with the same speed and in the same direction, unless acted upon by an external force.
In this scenario, the water bottle is at rest when you leave it in class, and when you return, it is still at rest. According to Newton's 1st Law, the water bottle will remain at rest unless an external force acts upon it.
Since there is no information provided about any external forces acting on the water bottle while you were away, it remained where you left it.
Learn more about Newton's 1st Law of Motion