A) Citrus fruits are generally not a concern for calcium oxalate stones. They are a good source of citrate, which may actually help prevent stone formation.

B) Dairy products are not specifically associated with calcium oxalate stones. However, high-calcium supplements might increase the risk, not dietary calcium from dairy products.

C) Red meat is not a significant concern for calcium oxalate stones. It is more associated with uric acid stones.

D) This is the correct answer. Leafy green vegetables are high in oxalates, which can contribute to calcium oxalate stone formation. Clients with calcium oxalate stones should limit their intake of these vegetables.