Father together with his good friends was________to go out for a camp________it began to rain. [ ]

A. hardly; than

B. around; as

C. about; when

D. nearly; while

下列组网形式中，保护通道可以传额外业务的有；（）

A.两纤单向复用段环

B.两纤双向复用段环

C.两纤单向通道环

D.四纤双向复用段环