Class 4     Subject  --S.St.    Chapter - 6    Waste Management       Tick the correct option:           1. Animals and plants waste can be converted into ----                 (a) Biogas         2. It is the duty of _____  to keep our surroundings clean and green.                 (b ) Both         3.  It is easy to recycle ------     (a)  Plastic         4.  Construction waste can be used for -----     (a)  Filling  ditches           B.    Fill in the blanks :     Human waste is open fields must be converted with soil  in rural areas.     Recycling is beneficial for the environment.     Biodegradable ...