Define a Python function named lastCharConcats which has 1 parameter. This parameter will be a list. Each entry in the parameter is a list of strs. Your function should use the accumulator pattern to create and return a list. The entry at index i in the returned list must be the concatenation of the strings in the list at index i of the input.

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)?