Although spinach is rich in calcium, it also contains a large amount of plasma oxalic acid which can effectively prevent the body's absorption of calcium. Therefore, if a person wants to consume enough calcium, he must replace it with other calcium-rich food or at least, eaten with spinach.
Rice does not contain calcium, but contains alkaline substances that neutralize plasma oxalic acid and change its properties, if true, can weaken the argument of the subject the most.