How do i get another's elements data from a element in a list?

    class Main
    {
        List<Ent> entis; // Contains EntA and EntB
    }
    abstract class Ent
    {
    }

    class EntA : Ent 
    {
        int Gold = 100;

        // How do i get the EntB class in the entis list from this class?
    }
    class EntB : Ent
    {
        float Position = 25.2f;
    }

    class Main
    {
        List<Ent> entis; // Contains EntA and EntB
    }
    abstract class Ent
    {
    }

    class EntA : Ent 
    {
        int Gold = 100;

        // How do i get the EntB class in the entis list from this class?
    }
    class EntB : Ent
    {
        float Position = 25.2f;
    }