Only eight out of China's 74 biggest cities passed the government's basic air quality standards in 2014, the environment ministry  (A) has said.The most polluted  (B) cities were in north- eastern Hebei.Beijing and Shanghai both failed the assessment, it (C) was based on measurements of major pollutants.China is attempting to cut pollution but  (D) the country still relies heavily on coal for its energy needs.The government shut more than 8,000 coal-burning factories in Hebei last year.But the BBC's Celia Hatton in Beijing says like many places in China, the authorities are struggling to balance factory closures with the demands of the country' s slowing economy.