Which of the following lists of ordered pairs is a function?
a. (1, 2), (4, 0), (3, 5), (4, 3)
b. (2, 5), (3, 6), (6, 9)
c. (2, 5), (3, 6), (2, 1)
d. (-1, 2), (2, 3), (3, 1), (2, 5)

To find if one is a function, you must see if the pattern is the same.
Domains (x) can not have two values
I forget what the y value is called, but there can be the same y- value for multiple      x - values

A. is not a function, because its ordered pairs are all over the place, and the value 4 in the x - value has two values assigned - 0 and 3, which makes it invalid.

B. may be a linear function. Its ordered pairs aren't jumping all over the place.
Both the x and y go up one for one, so the function could be y = x + 3

C. isn't because the x - value 2 has two values. Again, that makes this invalid.

D.  is invalid because there is two x - values for 2. 

Therefore, the answer is B.