The data for the number of hand$-$held gaming devices sold for the past $5$ weeks are $15$ units, $20$ units, $25$ units, $30$ units, and $17$ units respectively. The time series appears to be relatively stable, without trend, seasonal, or cyclical effects; thus, a moving average model would be appropriate. Setting k $=3$ the three$-$period moving average forecast for week $6$ is $\_\_\_\_\_\_\_\_.$

A$.$

$17$ units

B$.$

$30$ units

C$.$

$24$ units

D$.$

$20$ units