Which relation is a function?

A.
{(1, 2); (2, 3); (3, 4); (2, 5)}

B.
{(1, 2); (3, 2); (3, 3); (4, 2)}

C.
{(1, 2); (1, 3); (1, 4); (1, 5)}

D.
{(1, 2); (2, 3); (3, 4); (4, 5)}

Question

Which relation is a function?	
 
 A.
{(1, 2); (2, 3); (3, 4); (2, 5)}
 
 B.
{(1, 2); (3, 2); (3, 3); (4, 2)}
 
 C.
{(1, 2); (1, 3); (1, 4); (1, 5)}
 
 D.
{(1, 2); (2, 3); (3, 4); (4, 5)}

geerky42 · Answer

What do you think?

Function is relation where there is no such input (x-coordinate) that have two or more outputs (y-coordinate).

For example, it's not A because there is input 2 pairs with both outputs 3 and 5.

anonymous · Answer

Sorry, I already got the answer. I forgot to close this question.