Joey asked all of his friends how many times they visited the zoo this year. the dot plot shown here displays the responses that joey recorded. how many of joey's friends did not visit the zoo this year?

Which of the following best describes the graph below? + + 2 + 3 + 4 1 o a. it is not a function. o b. it is a one-to-one function. o c. it is a many-to-one function. o d. it is a function, but it is not one-to-one.