The horizontal line test is used to determine whether a function is _.

Mathwords: Horizontal Line Test. A test use to determine if a function is one-to-one. If a horizontal line intersects a function's graph more than once, then the function is not one-to-one. Note: The function y = f(x) is a function if it passes the vertical line test.           thats the best i got [;

the answer is 99.