What is the more secure alternative to the SMTP mail protocol?

Which of the following is a fully parenthesized expression?

a) x y + z b) (x y) + z c) ((x y) + z) d) (x) (y) + (z)

Queues that are implemented as arrays are called ________ queues.

A) dynamic B) stack C) static D) deque E) None of the above