Which structures are part of the body's first line of defense against pathogens? a. white blood cells b. red blood cells c. lymph nodes d. mucous membranes

Choice A. White blood cells is the correct answer.

"The first line of defence (or outside defence system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called neutrophils."

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