Answer
Model $C$ is unreasonable for the year 2020, giving a price of about ${{\$}} 9.94$ per gigabyte.
Work Step by Step
In 2020, $t=20$, and we find
$A(20)\approx 0.000014$
$B(20)\approx 0.1002$
$C(20)\approx 9.9438$
If we zoom out (set the view window to $[0,30] $ by $[0,10]$), we see that after $t=11$, graph C begins to rise steeply,
which is against our expectations for the price per gigabyte to decrease over time.
