The correct answer is: D. All of the above
Semiconductor memory was not available in the early days of computing, so central systems were used to store and process data. Memory was also very expensive and consumed a large amount of power, which made it impractical to use in individual devices. Central systems were able to overcome these limitations by sharing the cost of memory and power among multiple users.
Option A is correct because semiconductor memory was not available in the early days of computing. This meant that central systems had to use vacuum tubes or magnetic cores to store data, which were both very expensive and consumed a large amount of power.
Option B is correct because memory was very expensive in the early days of computing. This made it impractical to use memory in individual devices, as the cost would have been prohibitive. Central systems were able to overcome this limitation by sharing the cost of memory among multiple users.
Option C is correct because memory consumed a large amount of power in the early days of computing. This made it impractical to use memory in individual devices, as the power consumption would have been too high. Central systems were able to overcome this limitation by sharing the cost of power among multiple users.
Option E is incorrect because all of the above are correct reasons why central systems were used in the early days of computing.