Concept:The memory unit is the central working area of a computer where data and instructions are kept during processing.
Explanation:Before data can be processed, it must be placed in the main memory unit.
This memory unit holds the data, the instructions, and the intermediate results while the computer is working on them.
The monitor only displays the final output.
The floppy disk drive and hard drive are secondary storage devices, not the central working system.
Therefore, the memory unit is the main internal working system used for data processing.
Answer:D. Memory unit.