如下光纤种类，哪种最适合于开通高速DWDM系统（）。
A.G.652；
B.G.653；
C.G.654；
D.G.655。
参考答案：D
Sorry to have kept you waiting. You must have thought ___.
A．we are not coming
B．we were not coming
C．we did not come
D．we were not come
