中断
参考答案：
是指CPU在运行过程中，外部出现某种紧急事件，它请求CPU暂停现行程序的执行而转去处理此事件
There _____ many kinds of birds around here,
but now we seldom see them because of the air pollution. [ ]
A. use to
B. use to have
C. used to be
D. are
SPA协同凝集试验中抗体类别是
A．IgM
B．IgG
C．IgA
D．IgE
E．IgD
