The answer to you’re question is D.
Notice the "x" and "y" coordinates
the x-coordinate is well, the cosine value
the y-coordinate is well, the sine value
now the tangent
Use calculator soup on google it helps with fractions and whole numbers
https://www.google.com/url?sa=t&source=web&rct=j&url=http://baldwinfochtman.weebly.com/uploads/1/4/5/4/14541278/2.4_key.pdf&ved=2ahUKEwj9yI67iYDsAhWwxFkKHfMGDfIQFjABegQIARAB&usg=AOvVaw38O5aOofhocBcgS9ah9y_w
{(1, 0), (2, 0), (3, 0), (4, 0)}
{(1, 1), (2, 2), (3, 3), (4, 4)}
{(6, -6), (-6, 6), (5, -5), (-5, 5)}
These are all functions.