A stack is initially empty, then the following commands are performed: push 5, push 7, pop, push 10, push 5, pop, which of the following is the correct stack after those commands (assume the top of the stack is on the left)? A. 5, 10, 7, 5.
B. 5, 10.
C. 7, 5.
D. 10, 5.

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)?