There ____ great changes in our hometown in the last few years. [ ]

A. have had

B. have been

C. were

D. has been

下列关于紧凑技术的叙述中，哪个是不正确的

A．内存中任意一个程序都可以随时移动

B．移动可以集中分散的空闲区

C．移动会增加处理器的开销

D．采用紧凑技术时应尽可能减少移动的信息量