Answer: B. Graph B and Graph D
Explanation:
We'll use the vertical line test. This is where we try to draw a vertical line through more than one point on the graph. If such a task can be done, then the relation is said to fail the vertical line test. Furthermore, it means the relation is not a function.
Graph A is an example of this. We can draw a vertical line through 2 and have that vertical line cross the blue curve at more than one point. The input x = 2 leads to multiple outputs. Graph C is a similar story, but it only happens when x = 1.
Graphs B and D both pass the vertical line test. It's impossible to draw a single vertical line to cross through more than one point shown on their respective graphs. Any x input in the domain leads to exactly one y output, which in turn means we have functions here.
