There is external and internal so I'll list th external. The most important is skin then mucus, sweat or secretion, hair, nails and tears which are all part of the integumentary. Some internal defenses are white blood cells and T cells.
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Coefficients of Absorption for Common Materials
Perforated acoustic ceiling material 60%
Heavy curtains 50%
Carpeting 20%
Wood 5%
Plaster 3%
Clay tile 3%
Concrete 2%
The answer is C. Heavy curtains