What does the immune system protect the body against?

the immune system is the bodies defense against infection and illness  

the immune system is known to protect the body from foreign substances,cells,and tissues

try using substitution:

x + y - 6 = x - y. (i'm not giving you the exact answer). since 0 = x - y, then sub 0 in the equation with x - y. combine your like terms, and then use inverse operations, and you'll have your answer.

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