The correct answer is option 'D' - ball bearing.

Explanation:

Frictional resistance is the force that opposes the motion or relative motion of two surfaces in contact. It is caused by the interaction between the surfaces and depends on factors such as the nature of the surfaces, the applied load, and the relative motion between them.

In the case of low speeds, the frictional resistance in different types of bearings can be compared:

1. Journal bearing:
- A journal bearing consists of a rotating shaft and a stationary sleeve.
- The shaft is supported by a thin film of lubricating oil between its surface and the sleeve.
- The frictional resistance in a journal bearing is relatively higher compared to other types of bearings, especially at low speeds.
- This is because the entire surface area of the shaft is in contact with the sleeve, resulting in a larger contact area and higher frictional resistance.

2. Roller bearing:
- A roller bearing uses cylindrical rollers to reduce friction between moving parts.
- The rollers have a larger contact area compared to a ball bearing, resulting in higher frictional resistance.
- Therefore, a roller bearing would have a higher frictional resistance compared to a ball bearing at low speeds.

3. Ball bearing:
- A ball bearing consists of balls that roll between two rings to reduce friction.
- The balls have a smaller contact area compared to rollers, resulting in lower frictional resistance.
- At low speeds, the rolling action of the balls is more efficient, leading to lower frictional resistance compared to other types of bearings.

In summary, at low speeds, a ball bearing has the lowest frictional resistance compared to other options such as a journal bearing, roller bearing, or add questions (as mentioned in option C). This is because the rolling action of the balls in a ball bearing reduces the contact area and hence the frictional resistance.