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Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
According to the National Institute of Environmental Health Sciences, lung disease is the third leading killer in the United States, responsible for one in seven deaths. It is the leading cause of death among infants under the age of one year.
Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.