private void form1Load(object sender, EventArgs e) { checkFiles(); List <string> columns = client.Columns(); columns.RemoveRange(0, 8); var columns2 = client.Columns(); columns2.RemoveRange(0, 8); var columns3 = client.Columns(); columns3.Insert(0, "[Show All]"); columns3.RemoveAt(8); comboBox1.DataSource = columns3; comboBox2.DataSource = columns; comboBox3.DataSource = columns2; textBox1.Text = ""; textBox3.Text = ""; textBox4.Text = ""; }