Which of the following is a solid solution?

The structure of noble alloys can consist of solid solutions, in which the elements are completely soluble in one another at all temperatures and compositions. The majority of noble metal casting alloys for dental restorations are based on solid solutions. An important example is the palladium-silver (Pd-Ag) alloy system. Silver forms a series of solid solutions with palladium and gold, and is therefore common in gold- and palladium-based dental alloys. Ref: Phillip’s 12th edition page 79. Craig’s 14th edition page 182,184