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f is a function that maps $6-$bit binary strings to $4-$bit binary strings. For xin$\{0,1{\}}^6,f(x)$ is the string $x$ with the last two bits removed. Whi best describes the function $f?$

Bijection

$2-$to$-1$ correspondence

$4-$to$-1$ correspondence

$16-$to$-1$ correspondence