Drag and Drop C#

C#-Code: 
private void lstVereine_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
        {    
            if(lstVereine.Items.Count==0)
                return;
            string s = lstVereine.Items[lstVereine.IndexFromPoint(e.X,e.Y)].ToString();            
            DragDropEffects dde1=DoDragDrop(s,
                DragDropEffects.All);
            
            if(dde1 == DragDropEffects.All )
            {
                lstVereine.Items.RemoveAt(lstVereine.IndexFromPoint(e.X,e.Y));                
            }        
            
        }

private void lstAusgewählteVereine_DragDrop(object sender, System.Windows.Forms.DragEventArgs e)
        {
            if(e.Data.GetDataPresent(DataFormats.StringFormat))
            {                
                string str= (string)e.Data.GetData(DataFormats.StringFormat);
                lstVereine.Items.Add(str);                
            }
            
        }

private void lstAusgewählteVereine_DragOver(object sender, System.Windows.Forms.DragEventArgs e)
        {
            e.Effect=DragDropEffects.All;
        } 

this.lstAusgewählteVereine.DragOver += new System.Windows.Forms.DragEventHandler(this.lstAusgewählteVereine_DragOver);
this.lstAusgewählteVereine.DragDrop += new System.Windows.Forms.DragEventHandler(this.lstAusgewählteVereine_DragDrop); 

this.lstVereine.MouseDown += new System.Windows.Forms.MouseEventHandler(this.lstVereine_MouseDown); 

using System.Data;
using System.Data.SqlClient;

...

string connectionStr = ...

...

string queryStr =
  SELECT ProductName  +
  FROM Products JOIN Categories  + 
  ON Products.CategoryID = Categories.CategoryID  + 
  ORDER BY ProductName;

...

private void FillListBox1(string query) {
  SqlConnection connection = new SqlConnection(connectionStr);
  DataSet ds = new DataSet();
  SqlDataAdapter adapter = new SqlDataAdapter(query, connection);
  adapter.Fill(ds);

  foreach(DataRow dr in ds.Tables[0].Rows) {
    listBox1.Items.Add(dr[0].ToString());
  }
}

private void FillListBox1(string query )
		{
			SqlConnection connection = new SqlConnection(conString);
			DataSet ds = new DataSet();
			SqlDataAdapter adapter = new SqlDataAdapter(query, connection);
			adapter.Fill(ds);

			foreach(DataRow dr in ds.Tables[0].Rows) 
			{
				lstVereine.Items.Add(dr[0].ToString());
			}
		}

	string queryStr = SELECT tblMannschaften.Mannschaftsname  +
			FROM (tblMannschaften INNER JOIN tblKategorie  +
			ON tblMannschaften.[FK Kategorie_ID] = tblKategorie.[PK Kategorie_ID])  +
			WHERE (tblMannschaften.[FK Kategorie_ID] = ?);

		private void cmbKategorien_SelectedIndexChanged(object sender, System.EventArgs e)
		{					
			dataSet11.tblMannschaften.MannschaftsnameColumn.Table.Clear();
			con.Open(conString,null,null,0);
			FillListBox1(queryStr);
		}

string queryMansch = 
			SELECT Mannschaftsname  +
			FROM tblMannschaften  +
			WHERE [FK Kategorie_ID] =->;

private void FillListBox1(string queryMansch )
		{
			SqlConnection connection = new SqlConnection(queryMansch);
			DataSet ds = new DataSet();
			SqlDataAdapter adapter = new SqlDataAdapter(queryMansch, connection);
			adapter.Fill(ds);

			foreach(DataRow dr in ds.Tables[0].Rows) 
			{
				lstVereine.Items.Add(dr[0].ToString());
			}
		}

private void cmbKategorien_SelectedIndexChanged(object sender, System.EventArgs e)
		{					
			dataSet11.tblMannschaften.MannschaftsnameColumn.Table.Clear();
			con.Open(conString,null,null,0);
			FillListBox1(queryMansch + cmbKategorien.SelectedValue.ToString());
		}

private void FillListBox1(string queryMansch )
{
  SqlConnection connection = new SqlConnection(queryMansch);

public const string conString = Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\db1.mdb;

string queryMansch = 
			SELECT Mannschaftsname  +
			FROM tblMannschaften  +
			WHERE [FK Kategorie_ID] = ;

private void FillListBox1(string conString)
		{
			OleDbConnection connection = new OleDbConnection(conString);
			DataSet ds = new DataSet();
			OleDbDataAdapter adapter = new OleDbDataAdapter(conString, connection);
			adapter.Fill(ds);

			foreach(DataRow dr in ds.Tables[0].Rows) 
			{
				lstVereine.Items.Add(dr[0].ToString());
			}
		}

FillListBox1(queryMansch + cmbKategorien.SelectedValue.ToString());

private void FillListBox1(string queryMansch)
{
  OleDbConnection connection = new OleDbConnection(conString);
  OleDbDataAdapter adapter = new OleDbDataAdapter(queryMansch, connection);
  DataSet ds = new DataSet();
  adapter.Fill(ds);

  foreach(DataRow dr in ds.Tables[0].Rows) 
  {
    lstVereine.Items.Add(dr[0].ToString());
  }
}