Which of the following best describes a bijective function?

A$)$ It is both injective $($one$-$to$-$one$)$ and surjective $($onto$).$

B$)$ It is only injective $($one$-$to$-$one$).$

C$)$ It is only surjective $($onto$).$

D$)$ It is neither injective nor surjective.