下列用地中税法条例明确规定减免城镇土地使用税的是( )。

A．公园附设电影院使用的土地
B．市政街道绿化用地
C．纳税单位无偿使用免税单位的土地
D．个人所有的居住房屋和院落用地

The kernel is the (66) of an operating system such as Windows98, Windows NT, Mac OS or Unix. The kernel provides basic services for the other parts of the operating system, (67) it possible for it to run several programs at once (multitasking), read and write files and connect to networks and peripherals. Applications and utility programs use the services provided by the kernel to provide practical business functionality.

In operating systems such as Windows or most versions of Unix, the kernel (68) everything except application and utility programs.

In microkernel operating systems such as Digital Unix and Apples forthcoming Mac OS Server, the kernel (69) supports only multitasking and memory management. Other services such as applications, utilities and the user interface support device drivers, API and graphics which all (70) outside the microkernel.

（66）处填（）。

A．nucleus

B．center

C．core

D．heart