—Are there any computers on the desk?

—______ [ ]

A. Yes,  there are some.          

B. There are some.

C. Yes,  there are any.            

D. There are any.

某施工单位编制的某工程的单代号网络计划图如下所示，已知计划期等于计算工期。

上述网络计划的关键线路为( )。