The system unit can be referred to in different names. Some refer to this as the tower because of its size. Most people know this as “The Heart of the Computer” because it houses a lot of the parts that will make sure that computers can be used very well. Based on this, the answer is letter B.
There are certain items that should be available otherwise the computer will not work and the system unit has most of them such as the motherboard, the RAM, and all the other components of the computer that will make sure that this will be useful to a lot of people.