BEIJING, March 19 (AP) — A US-trained economist was appointed on Monday to succeed the longtime governor of China's central bank, Zhou Xiaochuan, at a time when the ruling Communist Party is trying to reduce financial risks and surging debt. The elevation of Yi Gang, a two-decade veteran of the central bank, to head the People's Bank of China was in a slate of promotions approved by China's ceremonial legislature of finance and economic officials as President Xi Jinping tightens control over government. Also Monday, the National People's Congress endorsed the appointment of Liu He, Xi's economic adviser, to a post as vice premier, where he is expected to oversee economic reform.