Chapter 8.4A, Problem 2A

Which of the following are function from the set $\left\{1,2,3\right\}\text{to be set }\left\{a,b,c,d\right\}$? If the set of ordered pairs is not a function, explain why not.

a. $\left\{\left(1,a\right),\left(2,b\right)\left(3,c\right),\left(1,d\right)\right\}$

b. $\left\{\left(1,a\right),\left(2,b\right),\left(3,a\right)\right\}$

c. $\left\{\left(1,a\right),\left(2,a\right),\left(3,a\right)\right\}$

d. $\left\{\left(1,a\right),\left(2,b\right),\left(3,b\right)\right\}$

e.

f.