Answer:
Option B.
Step-by-step explanation:
A relation is called a function if there exist unique value of y for each value of x.
In option (a), [tex]\{3,7,-7,9\}[/tex] is set not a relation.
In option (b), [tex]\{(3,9),(7,-4),(-7,7)\}[/tex] is function because there exist unique value of y for each value of x.
In option (c), [tex]\{(3,9),(7,-4),(3,7)\}[/tex] is not function because there exist two value of y, which are 9 and 7, for x=3.
In option (d), [tex]\{(3,9),(7,-4),(7,6),(-7,7)\}[/tex] is not function because there exist two value of y, which are -4 and 6, for x=7.
Therefore, the correct option is B.
