Which of the following is a common sign of infection?

Warmth at the site of infection is a classic sign of inflammation and infection. When the body experiences an infection, the immune system responds by increasing blood flow to the affected area, which often results in localized warmth. This is part of the body's natural response to combat the invading pathogens. Along with warmth, other signs of infection may include redness, swelling, and pain in the area.

The other options do not reflect typical signs of infection. Clear urine can indicate proper hydration and good kidney function but does not signify infection. Dry skin can result from various factors such as dehydration, environmental conditions, or certain medical conditions but is not a defined sign of an infection. Stable vital signs suggest the absence of acute stress or infection; typically, vital signs may become unstable or show abnormal changes during infection. Therefore, warmth at the site of infection is a reliable indicator of an inflammatory process in response to an infection.