Final answer:
OS X, also known as macOS, runs on a hybrid kernel, combining aspects of both monolithic kernels and microkernels for efficiency and modularity.
Step-by-step explanation:
The operating system (OS) known as OS X, which is developed by Apple Inc., utilizes a hybrid kernel. A hybrid kernel is a kernel architecture that includes elements of both monolithic kernels and microkernels.
This means that it has a core set of features running in the kernel space for efficiency, but it can also run some services in user space to provide better stability and modularity.
OS X, which has been rebranded as macOS, combines the Mach microkernel with components from FreeBSD's monolithic kernel. Therefore, the correct option from the given choices is b) hybrid kernel.