The correct answer is option 'C' - a hydraulic intensifier normally consists of a co-axial ram and two cylinders. Let's understand this in detail.

**Introduction to Hydraulic Intensifier:**
A hydraulic intensifier is a device that uses hydraulic pressure to increase the force or pressure of a fluid. It is commonly used in various applications where high pressure is required, such as hydraulic presses, machine tools, and hydraulic systems.

**Components of a Hydraulic Intensifier:**
A hydraulic intensifier typically consists of the following components:

1. **Co-axial Ram:** A co-axial ram is the main component of a hydraulic intensifier. It is a piston-like device that moves back and forth inside a cylinder. The movement of the co-axial ram is driven by hydraulic pressure.

2. **Two Cylinders:** The hydraulic intensifier has two cylinders. One cylinder houses the co-axial ram, while the other cylinder is used for fluid storage. These cylinders are interconnected and play a crucial role in the operation of the intensifier.

**Working Principle of a Hydraulic Intensifier:**
The working principle of a hydraulic intensifier involves the following steps:

1. **Initial Position:** In the initial position, the co-axial ram is at the bottom of the cylinder, and the fluid is stored in the other cylinder.

2. **Fluid Flow:** Hydraulic fluid is supplied to the cylinder containing the co-axial ram. The fluid applies pressure on the ram, causing it to move upwards.

3. **Fluid Displacement:** As the co-axial ram moves upwards, it displaces the fluid from the cylinder. This displaced fluid is redirected to the storage cylinder.

4. **Fluid Compression:** The co-axial ram continues to move upwards, compressing the fluid in the storage cylinder. This compression results in an increase in pressure.

5. **Increased Pressure Output:** The hydraulic intensifier's output is the high-pressure fluid stored in the storage cylinder. This high-pressure fluid can be used for various applications that require increased force or pressure.

**Advantages of a Hydraulic Intensifier:**
- Ability to generate high pressures without the need for large hydraulic pumps.
- Compact design and easy installation.
- Smooth and precise control over pressure.
- Suitable for applications where high force or pressure is required.

In summary, a hydraulic intensifier consists of a co-axial ram and two interconnected cylinders. The co-axial ram is responsible for displacing and compressing the fluid, while the cylinders provide the necessary space for fluid storage. This mechanism allows the intensifier to generate high pressures for various hydraulic applications.