Let A={1,2,3,4}. Which of the following binary relations defines a function from the set A ? If not, explain why. 1. f={(1,1),(2,2),(3,3),(4,4)} 2. ' f={(1,2),(2,3),(3,4)} 3. f={(4,2),(2,4),(3,4),(4,2)} 4. f={(1,4),(3,2),(2,3),(1,3),(4,2)} 5. f={(4,4),(1,4),(2,4),(3,4)} 6. f={(1,8),(2,1),(3,9),(4,6)}