Which of the following is one nonspecific defense against invaders to the body?

Mucous membranes serve as a key nonspecific defense mechanism in the body, providing a physical barrier against pathogens. These membranes line various cavities and organs, such as the respiratory and digestive tracts, and produce mucus, which traps dust, bacteria, and other foreign particles. This is an essential component of the innate immune system, which operates as a first line of defense, responding to any invader without the need for prior exposure or specific targeting.

In contrast, the other options represent specific or more targeted responses to pathogens. White blood cells are components of both the nonspecific and specific immune systems, but they often require more specific responses to effectively deal with infections. Vaccines work by training the immune system to recognize and respond to specific pathogens, thus falling under the category of acquired immunity. Antibodies are produced by the immune system in response to specific antigens and are part of the adaptive immune response, targeting specific invaders rather than broadly defending against all.