Script not showing up in edit>Project Settings> Script execution order

example of where the problem is from -
using UnityEngine;
using System.Collections;

[System.Serializable]
public class Item 
{
}

So this is script A, i have two others that i will call B and C.
i want to go into the script execution orer and run them in the order of A, B, C.
Now, as you can see, script A (the script above) won’t show up in the script execution orer because it doesn’t inherit MonoBehaviour. I can’t have it do that because then my “[System.Serializable]” won’t work properly, but i need them to execute in that order to avoid errors, how should i go about fixing this? i looked up several things and i’ve yet to find a solution besides add : MonoBehaviour back to the script (which i cant do in this case)

Thanks in advance!

If a script is not Monobehaviour-derived then Unity won’t call it, so it can’t control its execution order. You control its execution, by calling its functions when you want them.