Select the relations that are functions.

A. { (a, 1), (b, 1), (c, 1) }

B. { (a, a), (a, b), (a, c) }

C. { (1, a), (2, a), (3, a) }

D. { (a, a), (b, b), (c, c) }

Functions are, for every input there is 1 output

(x, y)

x is input

basically, x must never repeat with a different y

but y can repeat with different x's

(3,4) and (3,5) is not a function

but (3,4) and (5,4) is

look at them

I will assume a and b and c are different

A. a, b, and c are different so this is a function

B. A repeats with a, b, and c, not a function

C. 1 and 2 and 3 are different numbers so this is a function

D. a b and c don't repeat, this is a function

answer is A, C and D are functions