关于C#的代码，出现了转义范围问题

关于C#的问题，想问一下朋友们，下面的代码为啥会出现转义范围问题。错误代码CS8374

class Simple
{
    private int score=5;

    public ref int ReturnValue ()
    {

        return ref score;
       
    }

    public void PrintValue()
    {
        Console.WriteLine($"The score is {score}");
    }

}
class Program
{
    static void Main(string[] args)
    {
        int x = 2;
        int y = 3;
        Simple simple = new Simple();
        simple.PrintValue();
        ref int newScore = ref simple.ReturnValue();

        newScore = ref x;  //该代码会出现转义范围问题


        //如下步骤将不会产生转义范围问题
        //ref int newScore = ref x;
        //newScore = 7;
        //Console.WriteLine(x);
        //newScore = ref simple.ReturnValue();
        //newScore = 15;
        //simple.PrintValue();
        //newScore = ref y;
        //Console.WriteLine(newScore);


    }
}