单项选择题
A.Liquids with different viscosities will always have the same specific gravity
B.Liquids with different viscosities will never have the same specific gravity
C.Viscosity and specific gravity are directly proportional
D.Viscosity and specific gravity are not related in that one does not define or limit the other
单项选择题 Some chloronated flourocarbon refrigerants may decompose into a toxic irritating gas if it is （）.
单项选择题 A refrigeration system contaminated with moisture can be affected by （）.
单项选择题 R-12 is generally considered to be a safe, nontoxic, nonflammable, and non-explosive refrigerantIt can, however, become highly toxic when （）.