Which of the following is a factor affecting infection risk?

• A. Intact skin and mucous membranes
• B. Water filtration
• C. Exercise routine
• D. Sleep pattern

Answer: (A)

The main idea is that infection risk is greatly reduced by the body's first line of defense: intact barriers to entry. The skin and mucous membranes form a physical and chemical shield that prevents most microbes from entering the body. When these barriers are intact, pathogens have a hard time gaining a foothold. If the skin is broken or mucous membranes are damaged—through cuts, burns, ulcers, or invasive devices—the entry points for microbes open up, substantially increasing infection risk.

Other factors can influence infection risk in related ways, but they don’t provide the same direct barrier. Environmental controls like water filtration reduce exposure to pathogens in the surroundings. Regular exercise and adequate sleep can support overall immune function, which affects how the body handles infections, but they are not the immediate entry-point barrier that prevents infection in the same way intact skin and mucous membranes are.