President Hu Jintao said that the current "one country, two systems" arrangement between Hong Kong and the mainland must remain, as he officiated over celebrations to mark the 10th anniversary of Hong Kong's handover to China, the South China Morning Post reported. "One country is the prerequisite of two systems. Without one country, there will be no two systems. One country and two systems cannot be separated from each other," he said. Hu presided over the swearing-in ceremony of Chief Executive Donand Tsang for a new five-year term. That afternoon, some 20,000 protesters, including Cardinal Joseph Zen and Democrat Martin Lee, marched through central Hong Kong demanding full democracy.