What is the main function of the respiratory system? a. to exchange oxygen and carbon dioxide gases within the body b. to protect the body against foreign substances, such as bacteria and viruses c. to send signals from one part of the body to other parts of the body d. to break down food into nutrients that can be circulated throughout the body

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Life expectancy in the united states is (76.4 for men and 81.1 for women). life expectancy is not the same as healthy life expectancy. healthy life expectancy is the number of years a person is expected to live in this number is obtained by subtracting years spent in poor health from overall life expectancy. the world health organization (who) calculates healthy life expectancy in 194 countries. the united states ranks twenty-ninth in the world using this measurement, with an average of of healthy life expectancy. singapore ranks number one (76 years), and japan is number two (75 years).

Which many - celled organisms are capable of causing diseases in humans