Explanation:

First Class Lever:
- A first-class lever is a simple machine consisting of a rigid bar (see-saw) that is free to pivot on a fulcrum.
- In a first-class lever, the fulcrum is located between the effort (force applied) and the load (resistance).
- When one end of the lever is pushed down, the other end moves up, causing the load to move in the opposite direction.
- The force needed to lift the load is reduced because the lever multiplies the input force.

See-Saw as a First Class Lever:
- A see-saw is an example of a first-class lever where the fulcrum is placed in the center, with the load on one side and the effort (pushing or pulling) on the other side.
- When one person pushes down on their end of the see-saw, the other end moves up, causing the person on the opposite side to move upwards.
- The see-saw demonstrates the principles of a first-class lever by showing how a small force (effort) can lift a larger load.

Conclusion:
- In conclusion, a see-saw is classified as a first-class lever due to the positioning of the fulcrum, load, and effort in relation to each other.
- Understanding the different types of levers helps us comprehend how simple machines work and how they can be used to make tasks easier.

To determine whether a car jack is a screw or a lever, we need to understand the characteristics and functions of both.
Screw:
- A screw is a simple machine that consists of an inclined plane wrapped around a cylinder.
- It is used to convert rotational motion into linear motion.
- Screws are designed to hold objects together or to lift heavy loads by applying a twisting force.
Lever:
- A lever is a simple machine consisting of a rigid bar that rotates around a fixed point called a fulcrum.
- Levers are used to amplify or redirect force.
- There are three classes of levers: first, second, and third.
Now let's analyze the characteristics of a car jack and a see-saw to determine their classification:
Car Jack:
- A car jack is a mechanical device used to lift vehicles off the ground for maintenance or tire changes.
- It consists of a long rod or screw that is turned to raise or lower the lifting platform.
- The rod or screw in the car jack can be considered as an inclined plane wrapped around a cylinder, which aligns with the characteristics of a screw.
- Therefore, a car jack can be classified as a screw.
See-saw:
- A see-saw is a playground equipment consisting of a long plank balanced on a fulcrum.
- It is designed for two or more people to sit on opposite ends and take turns pushing off the ground to go up and down.
- The fulcrum in a see-saw acts as the pivot point, and the force applied by the users creates a rotational motion around the fulcrum.
- Based on the description, a see-saw can be classified as a first-class lever, where the fulcrum is located between the effort (force applied by the users) and the load (people sitting on the plank).
Therefore, the answer is b. First class lever, as a car jack is a screw and a see-saw is a first-class lever.