It shall contain a thermostatically controlled heat source mounted to the interior wall or on the backflow preventer to provide protection to -30oF.是什么意思_It shall contain a thermostatically controlled heat source mounted to the interior wall or on the backflow preventer to provide protection to -30oF.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句