MUMBAI -- India's capital re-opened schools and some building sites on Monday, amid signs of receding air pollution that authorities had deemed hazardous, although a toxic foam besmirched stretches of the Yamuna river flowing through New Delhi. The world's most polluted capital resumed its annual battle on pollution this month, despite government pledges to improve. Monday's air quality index (AQI) of 336 was down from Thursday's level of 509, but still "hazardous", Swiss group IQAir said. Children wore masks on the way to school, after a closure of nearly two weeks to protect them from pollution, while Hindu devotees celebrating a festival trudged through the smoggy ...Keep on reading: Indian capital resumes some activities despite hazardous air, river foam