Answer:
B. relation only
Explanation:
You want to have a description of the equation y² = x.
Relation
Any equation that represents a map between one or more input values and one or more output values can be called a "relation." The given equation maps x to two different output values for x > 0.
The equation can be described as a relation.
Function
A function is a relation that maps any given input value to exactly one output value. This relation maps most input values to two output values, so cannot be described as a function. (It fails the "vertical line test", which requires a vertical line intersect a function graph in one place at most.)