Final answer:
The correct sign of infection is redness in a body part, which is a result of the body's inflammatory response to pathogens involving increased blood flow and other protective processes.
Step-by-step explanation:
Redness in a body part is a sign of infection. When the body encounters pathogens, such as bacteria, it launches an inflammatory response as a defense mechanism. One of the cardinal signs of inflammation is redness, which is caused by increased blood flow to the affected area as blood vessels dilate. This process also leads to swelling, warmth, and pain, all of which serve to protect the body by drawing immune cells to the site of infection or injury.
It's important to monitor signs like increased redness, swelling, and pain after an injury to ensure proper healing and to check for potential infection. These signs indicate the body's ongoing battle against invading pathogens. Therefore, option b, redness in a body part, is the most accurate answer.