Explanation:

When we add two numbers in a computer program, we need to store the result somewhere. This location is called the destination address. There are several options for where we can store the result:

1. Immediate data: This is a value that is stored directly in the instruction itself. It is not a memory location or a register. However, this option is not suitable for storing the result of addition as it is a dynamic result.

2. Register: Registers are small, fast storage locations within the CPU. They can hold data that is being used frequently, such as variables or intermediate results. When we add two numbers, we can store the result in a register. However, registers have limited capacity, so we may need to use multiple registers or swap data in and out of memory.

3. Accumulator: An accumulator is a register that is specifically designed for arithmetic operations. When we add two numbers, we can store the result in the accumulator. This option is efficient because the accumulator is optimized for arithmetic operations.

4. Memory: Memory is a larger, slower storage location that can hold data that is not being used immediately. When we add two numbers, we can store the result in memory. This option is less efficient than using a register or accumulator because it requires more time to access the memory.

Therefore, the correct answer is option 'C' i.e., the destination address must always be the accumulator.