[单选] Not only the switches but also the old wiring ________ changed．

题目：[单选] Not only the switches but also the old wiring ________ changed．
A . have
B . are
C . have been
D . has been

正确答案：D
解析：
遇到not only．．．but also的句型时，谓语动词的单复数与靠近它的名词一致。Old wiring是单数，谓语动词为单数。选项D是正确的。句子大意：不光是开关，就连旧的线也换了。