The correct answer is option 'A': ROM and RAM.

Explanation:
Main memory, also known as primary memory or internal memory, is the storage area where data and instructions are stored for immediate access by the CPU (Central Processing Unit). It is an essential component of a computer system and is responsible for holding and transferring data and instructions between the CPU and other hardware devices.

There are two main types of main memory:

1. ROM (Read-Only Memory):
ROM is a type of memory that stores data permanently. It is called "read-only" because the data stored in ROM cannot be modified or erased by normal computer operations. ROM is non-volatile, meaning it retains its contents even when the computer is turned off. It contains instructions that are permanently written during the manufacturing process and cannot be altered or deleted by the user. These instructions are essential for the computer to start up and perform basic functions. Examples of ROM include firmware, BIOS (Basic Input/Output System), and microcode.

2. RAM (Random Access Memory):
RAM is a type of memory that stores data temporarily. It is called "random access" because the CPU can access any memory location directly, regardless of its location in memory. Unlike ROM, RAM is volatile, meaning it loses its contents when the computer is turned off. RAM is used by the CPU to store data and instructions that are currently being processed. It provides fast access to data, allowing the CPU to retrieve and store information quickly. RAM is further classified into two types: DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory).

Conclusion:
In summary, the two kinds of main memory are ROM and RAM. ROM stores data permanently and cannot be modified, while RAM stores data temporarily and provides fast access for the CPU. Both types of memory play crucial roles in the functioning of a computer system.