  It has been proved that almost all $n$-bit Boolean functions have exact
classical query complexity $n$. However, the situation seemed to be very
different when we deal with exact quantum query complexity. In this paper, we
prove that almost all $n$-bit Boolean functions can be computed by an exact
quantum algorithm with less than $n$ queries. More exactly, we prove that
${AND}_n$ is the only $n$-bit Boolean function, up to isomorphism, that
requires $n$ queries.
