Question

select the term to complete the sentence. white blood cells protect against and aid in blood clotting when injuries are sustained. antigens pathogen toxins

Explanation:

White blood cells (leukocytes) protect the body against pathogens (harmful microorganisms like bacteria, viruses, etc.). Antigens are substances that trigger an immune response, and toxins are harmful substances, but the primary role of white blood cells in protection is against pathogens. However, if we consider the options, "pathogen" (though the correct plural form in context might be "pathogens", but among the given options, "pathogen" is the term related to what white blood cells defend against. Wait, actually, let's re - check: White blood cells protect against pathogens (the agents causing disease) and also, platelets (not white blood cells) are more associated with blood clotting, but the question has a mix. But among the options, "pathogen" is the correct term for what white blood cells protect against. Wait, no, maybe I made a mistake. Wait, antigens are foreign substances that white blood cells respond to, but pathogens are the disease - causing agents. Wait, the options are antigens, pathogen, toxins. Let's think again. White blood cells (leukocytes) function in the immune system to defend against pathogens (bacteria, viruses, fungi, etc.). Antigens are molecules on pathogens (or other foreign substances) that trigger an immune response. Toxins are harmful substances, but the main target of white blood cell defense is pathogens. So among the given options, "pathogen" is the correct term to fill in the blank.

Answer:

pathogen