I’ll mark the correct answer asbr />

The answer is B. There can not be any alike "x" inputs.

In the point (x,y), x represents the domain of the function, and y represents the range of the function. A function is a part of a relation. In a relation, one domain can have multiple ranges. But in a function, one domain can not have multiple ranges. And in a function, multiple domains can have a range.

A function is a part of a relation. But a relation isn't always a function.
Function:
one domain only has a range, multiple domains can have one range

First option is not a function, it's a relation. Because one domain has multiple ranges ⇒ (0,3), (0,6)
Second option is a function! Because there's no multiple domains who have a range.
Third option is not a function, it's a relation. (1,4) and (1,6) is what makes it isn't a function.
Fourth option is not a function ⇒ (2,3), (2,6)

The answer is second option