Which relation is a function?

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

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

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

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

Question

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

anonymous · Answer

A function is a special relationship between values: Each of its input values gives back exactly one output value.

 It is often written as "f(x)" where x is the value you give it.

anonymous · Answer

Anyways it would be B (:

keeli_grace · Answer

How is it B? Would you please explain a little more?

keeli_grace · Answer

Is it because the domain numbers are all different?