private void Form1_Load(object sender, EventArgs e)
        {
            //Здесь заполняется первый набор данных, который загружается в ListBox

            oleDbDataAdapter1.Fill(dataSet11);

            listBox1.SelectedIndex = listBox1.Items.Count - 1;
           
        }

        private void listBox1_SelectedIndexChanged(object sender, System.EventArgs e)
        {
            dataSet21.Clear();

            if (listBox1.SelectedIndex != -1)
            {
                oleDbSelectCommand2.Parameters[0].Value = listBox1.SelectedValue;
                oleDbDataAdapter2.Fill(dataSet21);
            }
        }

  
         oleDbSelectCommand1.CommandText = "SELECT CustomerID, CompanyName FROM Customers WHERE (CompanyName LIKE ? + '%')";
         oleDbSelectCommand1.Parameters.Add(new System.Data.OleDb.OleDbParameter());
         oleDbSelectCommand1.Parameters[0].Value = "A";