Answer
one-to-one
Work Step by Step
A function $f$ is a one-to-one function if different values of the domain correspond to different values of the range.
($a\neq b$ implies $f(a)\neq f(b)$)
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The domain of f contains five values (years).
For no two different years do we have the same number of registered cars,
so the function is one-to-one
