Answer:
Option B.
Explanation:
A relation is called a function if there exist unique value of y for each value of x.
In option (a),
is set not a relation.
In option (b),
is function because there exist unique value of y for each value of x.
In option (c),
is not function because there exist two value of y, which are 9 and 7, for x=3.
In option (d),
is not function because there exist two value of y, which are -4 and 6, for x=7.
Therefore, the correct option is B.