Regarding OS structure, which of the following statements is false?

We refer the MS-DOSs structure as a simple one.

Unix has a kernel that provides functionalities for file system, CPU scheduling, memory management, and other operating-system functions. This kernel also contains some of the system software such as a C compiler.

In a Layered approach, functions can only call, per our book, functions of layers below the current layer.

In Mach, an example of microkernel structure, user models must use message passing to communicate.