The correct option is C Plastic bag
Petrol is made up of straight chain hydrocarbons which contains only H,C. As hydrogen and carbon are non-metals petrol is made of non metals.
Paper is made up of cellulose which has a chemical formula (C5H10O5)n. Cellulose consist of only C,H,O which are non-metals. So, paper is made up of non-metals
Plastic bags are made up of polyethylene which has a chemical formula (C2H4)n. Polyethylene has only C,H which are non-metals. So, plastic bags are made up of non-metals.
Common salt has a chemical formula NaCl which has sodium(Na) metal in it. So, common salt is not made up of only non-metals.