查了一下... :-)

來源: 於 2014-11-24 17:03:41 [博客] [舊帖] [給我悄悄話] 本文已被閱讀：次

"Radon Act 51 passed by Congress set the natural outdoor level of radon gas (0.4 pCi/L) as the target radon level for indoor radon levels. Unfortunately two-thirds of all homes exceed this level"... :-)