**Explanation:**

To understand why the correct answer is option 'D' (truncated conical pivot bearing), let's first understand what frictional torque is and how it is transmitted in a disc clutch.

**Frictional Torque in a Disc Clutch:**
- A disc clutch is a device used to transmit torque from one shaft to another by means of frictional forces.
- The frictional torque in a disc clutch is generated due to the contact between the clutch disc and the pressure plate.
- When the clutch is engaged, the pressure plate applies a uniform pressure on the clutch disc, causing it to be pressed against the flywheel.
- The frictional forces between the clutch disc and the flywheel generate the torque that is transmitted to the other shaft.

**Uniform Pressure Distribution:**
- The question mentions that the frictional torque is transmitted by a disc clutch with uniform pressure.
- Uniform pressure means that the pressure applied by the pressure plate on the clutch disc is constant across its entire surface.
- This implies that the contact pressure between the clutch disc and the flywheel is also uniform.

**Comparison with Different Bearing Types:**
Now, let's compare the frictional torque transmitted by a disc clutch with different bearing types:

1. **Flat Collar Bearing:**
- In a flat collar bearing, the contact surface between the collar and the pivot is flat.
- The pressure distribution in a flat collar bearing is not uniform.
- The contact pressure is higher at the center of the collar and decreases towards the edges.
- Due to the non-uniform pressure distribution, the frictional torque transmitted by a flat collar bearing will not be the same as that for a disc clutch with uniform pressure.

2. **Flat Pivot Bearing:**
- Similar to a flat collar bearing, a flat pivot bearing also has a flat contact surface.
- The pressure distribution in a flat pivot bearing is also non-uniform.
- Again, due to the non-uniform pressure distribution, the frictional torque transmitted by a flat pivot bearing will not be the same as that for a disc clutch with uniform pressure.

3. **Conical Pivot Bearing:**
- In a conical pivot bearing, the contact surface between the pivot and the bearing is conical.
- The pressure distribution in a conical pivot bearing is uniform.
- The contact pressure is constant across the entire contact surface.
- Therefore, the frictional torque transmitted by a conical pivot bearing can be the same as that for a disc clutch with uniform pressure.

4. **Truncated Conical Pivot Bearing:**
- A truncated conical pivot bearing is a modified version of a conical pivot bearing.
- It has a conical contact surface, but with a flat section at the center.
- The pressure distribution in a truncated conical pivot bearing is also uniform.
- The contact pressure is constant across the entire contact surface, including the flat section.
- Therefore, the frictional torque transmitted by a truncated conical pivot bearing can also be the same as that for a disc clutch with uniform pressure.

Based on the above explanations, we can conclude that the frictional torque transmitted by a disc clutch with uniform pressure is the same as that for a truncated conical pivot bearing.