Choose if each statement is true or false

{(1,2), (3,6), (4, -7), (6,-10)} is a function: true or false

{(1,1). (2,2), (3,3), (4,4)} is a function: true or false

{(1,3), (2,5), (7,9), (2,12)} is a function: true or false

{(1,8), (2,8), (3,8), (4,8)} is a function: true or false