The soldiers of Napoleon army while at Alps during freezing winter suffered a serious problem with regard to the tin buttons of their uniform. White metallic tin buttons get converted to grey poweder. This transformation is relate to

Options

A. an interaction with nitrogen of the air at very low temperatures
B. a change in the crystalline structure of tin
C. a change in the partial pressure of oxygen in the air
D. an interaction with water vapour contained in the humid air