How good are you at Call of Duty 4:Modern warfare

COD4 is a great game. Let's see if you are good at it while online

1 You see an enemy who doesn't know you're there. What do you do?
2 Having a sniper rifle, where do you hide?
3 When hiding with a sniper, what perk should you have?
4 When using an air-strike in the hardcore modes (friendly fire ON), what should you do?
5 When should you fire from the hip?