The correct answer is option 'C': the operating system.

The operating system is responsible for managing and controlling the hardware resources of a computer system. It provides a layer of abstraction between the application program and the underlying hardware, making the application program hardware independent.

Here is a detailed explanation of why the operating system can make the application program hardware independent:

1. Abstraction layer:
The operating system provides an abstraction layer that shields the application program from the hardware details. It presents a unified interface to the application program, hiding the complexities of different hardware architectures. This allows the application program to be written in a platform-independent manner.

2. Device drivers:
The operating system includes device drivers that enable communication between the application program and the hardware devices. These drivers handle the low-level details of interacting with specific hardware devices, such as printers, keyboards, or network cards. The application program can use the standardized interface provided by the operating system to access these devices, without having to worry about the specific hardware details.

3. Hardware resource management:
The operating system manages the allocation and sharing of hardware resources among multiple application programs. It ensures that each program gets fair access to the resources it needs, without interfering with other programs. This resource management includes memory management, CPU scheduling, and input/output operations. By providing this layer of abstraction, the operating system allows the application program to run on different hardware configurations without modification.

4. Portability:
Since the operating system provides a standardized interface to the application program, it enables portability across different hardware platforms. The same application program can run on different computers with different hardware configurations, as long as they are running the same operating system. This reduces the need for rewriting or modifying the application program for each specific hardware platform, saving time and effort.

In conclusion, the operating system plays a crucial role in making the application program hardware independent. It provides an abstraction layer, device drivers, hardware resource management, and portability, allowing the application program to run on different hardware configurations without modification.