Which substance is a polymer found in nature?
o carpet
o cotton
o paint
o nylon

B. Cotton

Explanation:

A polymer is a macro molecule or gaint molecule which is formed as a chain from  many small molecules(which is called as a monomer).

Polymer is a repeating unit of many monomers.

For example  

Ethylene or ethane formula is C2H4.

Many ethane molecules under particular temperature and pressure conditions undergo the polymerization process to form polyethene. During this process the double bond breaks and becomes single bond and produces a long chain which we call it as a polymer.

The repeating unit of Cotton polymer is called as Cellubiose which is made up of 2 glucose units.

The number of units which forms the polymer (degree of polymerization) is about 5000 cellubiose units.

a corroding iron, if that's one of your choices