(21) put computers to practical business use, but below the surface it is the heart of an (22) - the kernel - that provides the technical wizardry to juggle multiple programs, connect to networks and store (23) .
A traditional kernel provides all the functions for applications. The kernel (24) memory, I/O devices and parcels out processor time.
The kernel also supports (25) and fault tolerance, which is the ability to recover automatically when parts of the system fail.

A．manages

B．manage

C．managed

D．managing

PET