Which is true of veins?.

Naturally acquired active immunity occurs when the body produces antibodies in response to an infection or vaccine. This is not the case for antibodies passed through the placenta.

Choice B rationale:

Artificially acquired passive immunity involves the injection of antibodies, not the transfer through the placenta.

Choice C rationale:

Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. This does not describe the process of antibody transfer through the placenta.

Choice D rationale:

Natural passive immunity occurs when antibodies are passed from the mother to the fetus through the placenta. This matches the description in the question.

So, the correct answer is Choice D, after analyzing all choices.

Choice A rationale:

Lymph nodes do not produce lymphatic fluid, they filter it.

Choice B rationale:

Lymph nodes do not filter blood plasma to remove excess white blood cells. They filter lymphatic fluid to remove foreign invaders.

Choice C rationale:

While lymph nodes do contain cells that can produce antibodies, this is not their main function.

Choice D rationale:

The main function of lymph nodes is to filter lymphatic fluid and remove pathogens and foreign material.