Which relation is a function?

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

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

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

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

Question

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

anonymous · Answer

A function cannot have 2 different y values for the same x value.
For example, A is not a function because you can't have (1,2) AND (1,3)
There has to be only one y-value for x=1

anonymous · Answer

B is a function.

anonymous · Answer

is it 
D?

anonymous · Answer

@JoMary Give people an opportunity to work out problems on their own. I explained the concept. See if helpokandthankss understands first. Thanks

anonymous · Answer

Did you understand my explanation of why A is not a function?

anonymous · Answer

no it couldnt be D so its c or B right

anonymous · Answer

What do you think the answer is and why...please

anonymous · Answer

B

anonymous · Answer

why