The correct answer is D. Both (b) and (c).
An operating system is a software that manages the computer’s hardware and software resources and provides a platform for running application programs. It is required to run a microprocessor system because it provides the basic functions that are necessary for the computer to operate, such as managing the file system, memory, and processes. It also provides a structure with which to develop application programs by providing a set of APIs that application programs can use to access the computer’s resources. Finally, it is useful because standard modules can be used, which saves time and effort in developing application programs.
Option A is incorrect because it is not always required to run a microprocessor system. For example, some embedded systems do not require an operating system.
Option B is correct because an operating system provides a structure with which to develop application programs.
Option C is correct because an operating system is useful because standard modules can be used.
Option E is incorrect because both (b) and (c) are correct.