Which of the following is a common symptom of a computer virus?

Frequent crashes and slow operation is indeed a common symptom of a computer virus. When a virus infects a system, it can utilize system resources in ways that are detrimental to overall performance. This often leads to excessive use of CPU and memory as the virus performs its malicious tasks, such as replicating itself, stealing information, or disrupting normal operations. Consequently, users may experience sluggish performance, unresponsiveness, or complete system crashes when the virus is active.

In contrast, the other choices present outcomes that are not associated with a virus infection. Improved performance, increased storage capacity, and enhanced graphics quality would imply a functioning or upgraded system rather than one being compromised by a virus.