USD908205S20210119USD908205enS20210119USD908205SenD0908205US201729597383National20170316US20172959738320170316USUS201729597383FAir filtering mask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eanAirTek video, date unknown, qq.com, site visited Nov. 12, 2019.Amazon, Anti Pollution Face Mask for Dust, reviews 2019, https://www.amazon.com/Anti-Pollution-Dust-Mask-FILTERS/dp/B07NQKDNXL?th=1, Nov. 12, 2019.HWANG GWO-TZONGUSHwang, Gwo-TzongHWANG GWO TZONGUSHwang Gwo-TzongHWANG GWO TZONGUSHwang Gwo-Tzong