[Greek dockworkers fight with Greek riot police officers, during a demonstration in central Athens, Friday, April 8, 2016. The workers were protesting against the deal between Greece and China's shipping giant COSCO for the Athens port of Piraeus, which was signed on Friday. (AP Photo/Lefteris Pitarakis)]ATHENS, Greece (AP) — Greece signed an agreement Friday to sell a 67 percent stake in operating its biggest port to China's Cosco group, a significant step in the debt-crippled country's ambitious privatization drive.