请教大家一个NP问题?

You are configuring a totally stubby area in OSPF.What configuration must the ABR have that are not required on internal area routers?

A. A virtual link to area0
B. OSPF summarization command
C. default-cost extension to the area command
D. no-summary extension to the area stub command
我觉得选D，TK答案选A，有些人也认为是A
因为在完全末节区域，只在ABR上配
con#area stub on summary
其他路由器配
con#area stub 所以我认为选A，望各大虾不吝赐教！