You are presented with the question "What causes rust?" and the following answer choices: 
- a pathogens
 - Roundworms
 - flow of electrons
 - dust
 - thunder
 - an amoebae
 - chemical weathering
 - skin

Now knowing that chemical weathering causes iron in rock to oxidize and rust colored residues are due to oxidized iron, choose the best answer.


 

       chemical weathering  