When a foreign substance invades the body, which statement best describes the body's response?

• A. protect itself
• B. go on alert
• C. attempt to inactivate the foreign substance
• D. All of these answers are correct

Answer: (D)

When a foreign substance enters, the body mounts a coordinated defense that includes protection, alert, and neutralization. Protection comes from barriers like skin and mucous membranes and from ready innate defenses that respond quickly. The body also goes on alert, using signaling molecules to summon immune cells and trigger inflammation and fever to contain the threat. It then attempts to inactivate the invader through mechanisms such as phagocytosis by immune cells and antibodies that neutralize or destroy pathogens. Because all of these elements work together, describing the response as encompassing protection, alert, and inactivation best captures what's happening.