During a pre-flight inspection, you notice that several of the rivets on the upper wing structure have a black residue streaming back behind the rivets and the residue is also streaming back from the seams between pieces of aluminum that make up the wing skin. Group of answer choices This is normal, especially during a drought when airplanes are not washed This is an indication of fretting corrosion and is the result of the two aluminum pieces rubbing together after being severely overstressed This is an example of filiform corrosion and is normal This is an example of galvanic corrosion and should be evaluated by an airframe mechanic