A laser printer keeps producing vertical black lines running down the page. This issue is MOST LIKELY to be cause by which of the following components?

Vertical black lines going down all or part of the page might be caused by a groove or scratch in the EP drum. A scratch receives less (if any) charge than the other areas since it is lower than the surface. As a result, toner sticks to it as if it were discharged. The groove may extend all the way around the circumference of the drum, allowing the line to go all the way down the page.