如何使用ctrl键+鼠标单击来选择多个控件

可能这个问题已经有答案了，但我没能找到它。我有一个tabControl与flowlayoutpanel在每个选项卡页面，我可以在运行时添加控件。我可以重新排列它们，在标签页之间移动它们。我如何选择多个控件，以便能够使用ctrl键+鼠标单击来移动它们?

这是目前为止我的拖动事件:

private void control_DragDrop(object sender, DragEventArgs e)
    {
        Control target = new Control();
        target.Parent = sender as Control;
        if (target != null)
        {
            int targetIndex = FindCSTIndex(target.Parent);
            if (targetIndex != -1)
            {
                string cst_ctrl = typeof(CustomControl).FullName;
                if (e.Data.GetDataPresent(cst_ctrl))
                {
                    Button source = new Button();
                    source.Parent = e.Data.GetData(cst_ctrl) as CustomControl;
                    if (targetIndex != -1)
                        fl_panel = (FlowLayoutPanel)tabControl1.SelectedTab.Controls[0];
                    if (source.Parent.Parent.Name == target.Parent.Parent.Parent.Name)
                    {
                        this.fl_panel.Controls.SetChildIndex(source.Parent, targetIndex);
                    }
                    else
                    {
                        target.Parent.Parent.Parent.Controls.Add(source.Parent);
                        this.fl_panel.Controls.SetChildIndex(source.Parent, targetIndex);
                    }
                }
            }
        }
    }
    private int FindCSTIndex(Control cst_ctr)
    {
        fl_panel = (FlowLayoutPanel)tabControl1.SelectedTab.Controls[0];
        for (int i = 0; i < this.fl_panel.Controls.Count; i++)
        {
            CustomControl target = this.fl_panel.Controls[i] as CustomControl;
            if (cst_ctr.Parent == target)
                return i;
        }
        return -1;
    }