Final answer:
The seesaw is an example of a first-class lever where the fulcrum is in the middle and the effort force and the load are on opposite sides.
Step-by-step explanation:
A first-class lever is a simple machine where the fulcrum is located between the effort force and the load. In the case of the given options, the seesaw is the example of a first-class lever. The fulcrum is located in the middle, the effort force is applied on one side by pushing or pulling, and the load is on the other side.
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