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immune system –n. the system that protects your body from diseases and infections
tumor –n. a mass of tissue found in or on the body that is made up of abnormal cells
bold –adj. not afraid of danger or difficult situations
extraordinary –adj. extremely good or impressive
obstacle –n. a problem that makes it difficult to reach a goal; a barrier
variant –n. something that is different in some way from others of the same kind
rigid –adj. unwilling to lower requirements or compromise quality
credit –n. praise or special attention that is given to someone for doing something or for making something happen
acknowledge –n. the act of showing that you know, admit, or accept that something exists or is true
