向主窗体中加A窗体
{
                bool isExitFormConfig = false;//判断配置窗口是否已经打开，防止重复打开多个配置窗口
                foreach (Form openForm in Application.OpenForms)
                {
                    if (openForm.Name == "A")
                    {
                        openForm.Visible = true;//如果配置窗口已打开则将其显示
                        openForm.Activate();//并激活该窗体
                        isExitFormConfig = true;
                        break;
                    }
                }
                if (!isExitFormConfig)
                {
                   A fc = new A();
                    fc.TopLevel = false;//将被更改以使该窗体成为具有工具窗口边界的非顶级窗体。

                    fc.Dock = DockStyle.Fill;
                    this.panel1.Controls.Add(fc);//this是你的主窗口
                    fc.Show();
                    fc.TopMost = true;
                }
            }
}

向主窗体中加B窗体

{
                bool isExitFormConfig = false;//判断配置窗口是否已经打开，防止重复打开多个配置窗口
                foreach (Form openForm in Application.OpenForms)
                {
                    if (openForm.Name == "B")
                    {
                        openForm.Visible = true;//如果配置窗口已打开则将其显示
                        openForm.Activate();//并激活该窗体
                        isExitFormConfig = true;
                        break;
                    }
                }
                if (!isExitFormConfig)
                {
                   B fc = new B();
                    fc.TopLevel = false;//将被更改以使该窗体成为具有工具窗口边界的非顶级窗体。

                    fc.Dock = DockStyle.Fill;
                    this.panel1.Controls.Add(fc);//this是你的主窗口
                    fc.Show();
                    fc.TopMost = true;
                }
            }
}

帮忙看一下代码，加载A窗体后，加载后面的窗体B不能出现在最上层
如何改才能让后来出现的子窗体B在最前层显示？