是什么导致了'不一致的可访问性'下面的代码有错误

错误:

错误1不一致的可访问性:字段类型'System.Collections.Generic.List<Lines>'比field更难接近'Star.lines' J:' documentation 'Universiteit Utrecht - Game技术/模型/系统Ontwikkeling'Assignment4'ShapeDrawing'ShapeDrawing' stars .cs 15 24 ShapeDrawing

导致错误的代码:

public class Star : Shape
{
    private int x;
    private int y;
    private int width;
    private int height;
    public List<Lines> lines; // TODO: Ask explanation for cause of error. 
    public Star (int x, int y, int width, int height)
    {
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
    }
    public override void CalculateGeometry()
    {
        lines = new List<Lines>();
        int numPoints = 5;
        Point[] pts = new Point[numPoints];
        double rx = width / 2;
        double ry = height / 2;
        double cx = x + rx;
        double cy = y + ry;
        double theta = -Math.PI / 2;
        double dtheta = 4 * Math.PI / numPoints;
        int i;
        for (i = 0; i < numPoints; i++)
        {
            pts[i] = new Point(
                Convert.ToInt32(cx + rx * Math.Cos(theta)),
                Convert.ToInt32(cy + ry * Math.Sin(theta)));
            theta += dtheta;
        }
        for (i = 0; i < numPoints; i++)
        {
            lines.Add(new Lines(pts[i].X,
                                pts[i].Y,
                                pts[(i + 1) % numPoints].X,
                                pts[(i + 1) % numPoints].Y));
        }
    }
}

我已经试着调查这个错误的原因。它似乎是由公共类使用的公共字段引起的。在这种情况下，似乎方法和字段都是公共的，所以我不确定问题是什么。

事先感谢任何帮助。