suppose we have two implementations of the same instruction set architecture. computer A has a clock rate of $4$ GHz and a CPI of $4\mathrm{.}0$ for same program. computer B has a clock rate of $5$ GHz and a CPI of $2\mathrm{.}5$ for the same program. the CPU time for program A equals:

$*$

$2\mathrm{.}5$ I nseconds

$1$ I nseconds

$4$ I nseconds

$0\mathrm{.}5$ I nseconds