CHINESE President Xi Jinping said he would support Chinese firms that invest in Angola's agriculture and manufacturing sectors, state media reported on Friday, as the African oil-producing nation seeks help in diversifying its economy. "The Chinese side is willing to work with Angola to implement key infrastructure projects and support strong Chinese companies to go to Angola to carry out various forms of cooperation," Xi told visiting Angolan President Joao Lourenco at the Great Hall of the People in Beijing. Lourenco's visit follows Angola's announcement in December it would leave producer group the Organization of the Petroleum Exporting Countries and agreements with…