书上的一个例子，我照着输入程序，运行时出现“无法在 DLL“gdi32”中找到名为“SetBKMode”的入口点”
请问是什么原因啊？
using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;
namespace circlewindow
{
   
    public partial class Form1 : Form
    {
        [System.Runtime.InteropServices.DllImport("gdi32")]
        private static extern IntPtr BeginPath(IntPtr hdc);
        [System.Runtime.InteropServices.DllImport("gdi32")]
        private static extern int SetBKMode(IntPtr hdc, int nBKMode);
        const int TRSPARENT = 1;
        [System.Runtime.InteropServices.DllImport("gdi32")]
        private static extern IntPtr EndPath(IntPtr hdc);
        [System.Runtime.InteropServices.DllImport("gdi32")]
        private static extern IntPtr PathToRegion(IntPtr hdc);
        [System.Runtime.InteropServices.DllImport("gdi32")]
        private static extern int Ellipse(IntPtr hdc, int x1, int y1, int x2, int y2);
        [System.Runtime.InteropServices.DllImport("user32")]
        private static extern IntPtr SetWindowRgn(IntPtr hdc, IntPtr hRgn, bool bRedraw);
        [System.Runtime.InteropServices.DllImport("user32")]
        private static extern IntPtr GetDC(IntPtr hWnd);
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            IntPtr dc;
            IntPtr region;
            dc = GetDC(this.Handle);
            BeginPath(dc);
            SetBKMode(dc, (int)TRSPARENT);
            Ellipse(dc, 20, 20, 220, 220);
            EndPath(dc);
            region = PathToRegion(dc);
            SetWindowRgn(this.Handle, region, true);
        }
    }
}

问题解决了，DllImport("gdi32")变为DllImport("gdi32"，EntryImport="BeginPath")就行了。