Based on
The primary reason multiprogramming operating system was developed and the reason they are popular, is that they enable the CPU to be utilized more efficiently. If the operating system can quickly switch the CPU to another task whenever the being worked in requires relatively slow input, output or storage operations, then CPU is not allowed to stand idle.
This mean that more can be accomplished a given amount of time. For example, if a disk drive that task can be delegated to channel and the CPU can be put to work in another program while the data are being read in multiprogramming is thus an effective way the fast-working CPU most busy with computations while slower input, output and storage operation are being carried out.
D will be correct choice