Crevices can be either metal-to-metal or metal-to-nonmetal and can be formed under deposits of debris or corrosion products.

• A. Metal-to-metal only
• B. Metal-to-nonmetal only
• C. Metal-to-metal or metal-to-nonmetal
• D. Nonmetal-to-nonmetal

Answer: (C)

Crevice corrosion happens when a narrow gap traps electrolyte and creates different conditions inside the crevice than outside, leading to localized attack on the metal surface. This can occur at a metal-to-metal interface (two metal surfaces in contact) or at a metal-to-nonmetal interface (a metal in contact with a nonmetal such as a deposit, paint, scale, or debris). Debris or corrosion products within the crevice further restrict flow and oxygen supply, intensifying the attack. So the statement is correct because crevices form in both metal-to-metal and metal-to-nonmetal situations and can develop under deposits or corrosion products. The other options miss one of the possible interfaces or describe a non-applicable scenario, making them incomplete.