有关变态反应的描述正确的是（）

A．与药量无关

B．在特异体质患者身上发生

C．每个患者所发生的变态反应症状都相同

D．患者有药物过敏史

E．反应性质与药物作用一致

Inside the computer, the operation system (of another software module called a data communication (71) )must decide which program will get control next. Each program remember, is associated (72) . a particular front -end port. If a program’s data have not yet reached its front - end buffer, there is no point giving that program control. Thus the data communication monitor sends its own (73) signal to the front -end devices next port is polled. Note that the (74) computer speed. The computer never has to wait for a terminal or a communication line. Instead, it is the expressive front - end processor that waits for the slower system (75) to respond.

（73）处填（）。

A.palling

B.pulling

C.polling

D.isolate