Question 787139
<pre>
A function cannot contain two ordered pairs with the same first coordinate.</pre>
A. {(5, 2), (3, 2), (4, 2), (5, 1)}<pre>
This is not a function because (5,2) and (5,1) are 
two ordered pairs with the same first coordinate 5.</pre>
B. {(1, 2), (1, 3), (2, 1), (3, 4)}<pre>
This is not a function because (1,2) and (1,3) are 
two ordered pairs with the same first coordinate 1.</pre>
C. {(1, 3), (2, 6), (3, 8), (1, 7)}<pre>
This is not a function because (1,3) and (1,7) are 
two ordered pairs with the same first coordinate 1.</pre>
D. {(1, 4), (8, 9), (10, 11), (12, 12)}<pre>
This is a function because all the ordered pairs 
have different first coordinates.

Edwin</pre>