using System.Globalization;
using System.Linq;
List<string> TheMonths = DateTimeFormatInfo.CurrentInfo.MonthNames.Take(12).ToList();
comboBox1.DataSource = TheMonths;
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
Console.WriteLine("{0}: {1}", comboBox1.SelectedIndex, comboBox1.SelectedValue);
}
Run code: observe.