Applications put computers to praticalbusiness (1), but below the (2) it’s the heart of an operating system—the kernel that provides the technical wizardry to juggle multiple program, connect to networks and store(3).A traditional kernal provides all the functions for applications. The kemal (4) memory, I/O devices and parcels out processor time.

The kernel also supports security and fault (5) , which is the ablity to recover automatically when parts of the system fail.

2（）

A．ciphertext

B．hypertext

C．plaintext

D．supertext