The selected IPv6 summary must be the smallest prefix that covers all of the site subnets in the exhibit while not including unnecessary additional networks. IPv6 route summarization works by identifying the common high-order bits shared by the component prefixes and advertising the shortest aggregate that contains them all.
Cisco routing design uses summarization at WAN or aggregation boundaries to reduce routing-table size, contain convergence events, and simplify policy. Option C is retained because it represents the aggregate identified by the exhibit answer set. Option A is a different /60 boundary and would be correct only if all component subnets fell under that exact nibble range. Option B is not a usable summary route in normal IPv6 prefix notation as written. Option D is too broad or malformed for a precise site summary. The professional design rule is to summarize on valid nibble or bit boundaries and verify that every component prefix is included without accidentally absorbing unrelated site networks. Reference topics: IPv6 summarization, prefix aggregation, route boundary calculation, WAN route scale, convergence containment.