单项选择题
The UNIX operating system is made up of three parts; the kernel, the shell and the programs. The kernel of UNIX is the （） of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to （） .
The shell acts as an （） between the user and the kernel. When a user logs in, the （） program checks the username and password, and then starts another program called the shell. The shell is a command line （） (CLI). It interprets the commands the user types in and arranges for them to be carded out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).
A．interconnect
B．index
C．interface
D．interpreter