The correct answer is A) when a low-stock situation occurs and minor corrections are made. The reasoning is that a revised print of a chart is typically made when there is a low-stock situation, meaning the current version of the chart is running low, and only minor corrections or updates need to be made. This is a more cost-effective approach than reprinting the entire chart from scratch. The other options are not correct because: B) magnetic variation is typically updated annually, not every two years; C) a revised print would be made for more extensive corrections, not just minor ones; and D) a revised print is not necessarily made after every major hydrographic survey, as the survey data may not warrant immediate changes to the chart.