Final answer:
The main memory in a computer system accommodates the operating system, the CPU, and user processes, meaning the correct response is 'All of these'.
Step-by-step explanation:
The main memory in a computer system is a critical hardware component that performs various functions. It serves as a storage area for the operating system, which is loaded into the main memory from the storage device when the computer is turned on. The central processing unit (CPU) utilizes main memory to fetch instructions, execute them, and store intermediate results. Additionally, the main memory is used to store user processes, which are the programs currently being executed and their associated data. Therefore, in response to the question, the main memory accommodates all of the following: a) Operating system, b) CPU, and c) User processes. This means that the correct answer is d) All of these.