单项选择题
（）can give a hard-wearing surface and the required color.
A.Primers B.Undercoats C.Topcoats D.Cement wash
单项选择题 Undercoats are used （）the primer before the topcoat.
单项选择题 Primer coats are applied to a bare metal surface to （）protection against rust.
单项选择题 Primer coats are applied to a bare metal surface to give protection against （）.
