Examine the following relation and state whether it is a function or not,giving reasons:
$R = \{(2, 1), (3, 1), (4, 2)\}$

• A
  It is a function because each element in the domain has a unique image.
• B
  It is not a function because the element $1$ is repeated in the range.
• C
  It is not a function because the element $2$ is repeated in the domain.
• D
  It is not a function because the relation is not one-to-one.