What is the proper command to perform an Nmap XMAS scan every 15seconds?

Q. What is the proper command to perform an Nmap XMAS scan every 15seconds?

A.            nmap -sX -sneaky

B.            nmap -sX -paranoid

C.            nmap -sX -aggressive

D.            nmap -sX -polite

Answer: nmap -sX -sneaky