Which statement indicates that the transmission of a message was secure and that no one tampered with the message? ОА.
The receiver's private key matches the sender's public key,
OB.
The sender's digital signature matches the receiver's digital signature.
O C.
The sender's public key matches the receiver's public key.
OD
The hash generated by the receiver from the message matches the hash of the sender.

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)?