单项选择题
On a（）memory system，the logical memory space available to the program is totally independent of the physical memory space.
A．cache B．virtual C．RAM D．ROM
单项选择题 A programmer must know about a function’s（）to call it correctly.
单项选择题 One solution to major security problem is（），which are frequently installed to fix known security holes.
单项选择题 （）is a clickable string or graphic that points to another Web page or document.
