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Chapter 23, Lesson 3, Reteaching Activity. False. The body’s physical barriers include the skin, the mucous mem-branes, and cilia. The body’s chemical barriers include tears, saliva, and gastric juice. True. The immune system includes a great variety of cells, tissues, organs, and chemicals, including phagocytes, lymphocytes, and the lymphatic system. False. The immune system has two ... ................
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