Students to get cash for picking up trash   SINGAPORE'S parks and nature reserves could become ""shells'' of what they are today, if people do not learn to put rubbish in bins. The warning came yesterday from the deputy chairman of the Government Parliamentary Committee for the Environment, Associate Professor Low Seow Chay, at the launch of a campaign to make people more environmentally aware. Called Cash For Trash, it is a week-long, island-wide clean-up of parks and nature reserves and is part of the Environment Ministry's 11th Clean and Green Week. During this period, about 10,000 students from over 60 primary and secondary schools will pick up litter from public areas. Every bag of rubbish they collect means money from the event's sponsors for their schools' kitties, so they can initiate their own eco-projects. Canossa Convent Primary School and Kampong Ubi Citizens' Consultative Committee Happy Gardens Area sub-committee also formally adopted Aljunied Park at Aljunied Road yesterday. The National University Hospital also did its bit for the environment. Seventeen of its senior managers and clinical staff spent part of yesterday morning planting 15 mango trees by the hospital's Kent Ridge Wing.