Which of the following refers to data that is typically numeric or categorical; can be organized and formatted in a way that is easy for computers to read, organize, and understand; and can be inserted into a database in a seamless fashion? A. Structured data B. Unstructured data C. Web scraping D. Artificial intelligence E. Machine learning

Suppose there is a relation r(a, b, c) with a b+-tree index with search keys (a, b).1. what is the worst-case cost of finding records satisfying 10 < a < 50 using this index, in terms of the number of records n1, retrieved and the height h of the tree? 2. what is the worst-case cost of finding records satisfying 10 < a < 50 and 5 < b < 10 using this index, in terms of the number of records n2 that satisfy this selection, as well as n1 and h defined above? 3. under what conditions on n1 and n2, would the index be an efficient way of finding records satisfying the condition from part (2)?