official answer given is (B)Heap.
Let n be the number of pages visited by the search engine at the time a query is submitted. Assume that it takes constant time to compute the relevance score for each page w.r.t. a query. Then it takes O(n) time to compute the relevance scores, a further O(n) time to build a heap of n relevance scores, and O(k · log n) time for k delete-max operations to return the top k scores.
(from cmi answer key)