SHANGHAI, Jan 14 (Reuters) - China’s copper imports in December fell for a third straight month, customs data showed on Thursday, as construction and manufacturing demand was not enough to offset the closure of an arbitrage window that made 2020 a record year for shipments. Arrivals of unwrought copper and copper products into China, the world’s top copper consumer, were 512,332 tonnes last month, the General Administration of Customs said. That was down from 561,310.7 tonnes in November, and also down from a year earlier. (Reporting by Emily Chow; Editing by Christian Schmollinger)