The correct answer is option 'B' - Inclined plane.

An inclined plane is a simple machine that is a flat surface with one end higher than the other. It allows objects to be moved from a lower position to a higher position with less force. In the case of a bath tub, the floor of the tub is sloped or inclined, allowing water to drain out easily.

Here is an explanation of why an inclined plane is the correct answer:

1. Definition of an inclined plane:
- An inclined plane is a simple machine that consists of a flat surface with one end higher than the other.
- It is used to move objects from a lower position to a higher position with less force.

2. The floor of a bath tub as an inclined plane:
- If you observe the floor of a bath tub, you will notice that it is sloped or inclined towards the drain.
- This sloped surface allows water to flow towards the drain and be drained out of the tub.
- The inclined plane of the tub floor reduces the effort required to drain the water, as the water naturally flows down the slope due to gravity.

3. Function of the inclined plane in a bath tub:
- The inclined plane in a bath tub helps in the drainage of water.
- When the plug is removed, the water on the sloped surface of the tub floor flows towards the drain.
- The angle of the slope helps to create a downward force on the water, allowing it to flow more easily.

4. Advantages of using an inclined plane in a bath tub:
- The use of an inclined plane in a bath tub makes it easier to drain water.
- It reduces the effort required to remove the water from the tub.
- The sloped surface allows the water to flow naturally towards the drain, without the need for additional force or energy.

In conclusion, the type of simple machine found on the floor of a bath tub is an inclined plane. The sloped surface of the tub floor allows water to drain out easily by utilizing the force of gravity.