To determine which diagram represents a function, we need to follow the definition of a function: each input must correspond to exactly one output. This means that for every input value, there should be only one arrow pointing to an output value.

Let's analyze each diagram:

1. Top diagram: Some input values (e.g., 0 and 2) have arrows pointing to multiple outputs, which violates the definition of a function.
2. Middle diagram: Each input corresponds to a unique output. No input has more than one arrow, which satisfies the definition of a function.
3. Bottom diagram: Some inputs have arrows pointing to multiple outputs, which again does not meet the function criteria.

Therefore, the middle diagram shows a function.

Would you like further details on this topic or have any questions?

Here are five related questions to deepen your understanding:

1. What is the definition of a function in mathematics?
2. How can you identify if a graph represents a function using the vertical line test?
3. What are examples of functions that are commonly used in real life?
4. Can a function have two different inputs with the same output? Why or why not?
5. What distinguishes a one-to-one function from other types of functions?

Tip: A function ensures a unique output for every input, but multiple inputs can share the same output.