C# 泛型类型的父子类转换

我有三门课，分别是OptionFeature、Fabric和Material

织物是材料的子类

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现在我有一个OptionFeature类型的对象。如何将此对象转换为OptionFeature

    class Program
    {
        static void Main(string[] args)
        {
            OptionFeature optionFeature = new OptionFeature();
            optionFeature.material = new Material();
            Fabric fabric = (Fabric)optionFeature.material;
            List<Material> materials = new List<Material>();
            List<Fabric> fabrics = materials.Select(x => (Fabric)x).ToList();


        }
    }
    public class OptionFeature
    {
        public Material material {get;set;}
    }
    public class Material
    {
    }
    public class Fabric : Material
    {
    }​

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泛型差异仅支持接口和委托，不支持类。