namespace DateTimeLibrary { using System; using System.Collections; public class DateTimeLibrary { public static string FirstDayOfCurrentMonth() { DateTime today = DateTime.Today; DateTime time2 = new DateTime(today.Year, today.Month, 1); return time2.ToShortDateString(); } public static string FirstDayOfCurrenttQuarter() { DateTime time2; DateTime time3; DateTime today = DateTime.Today; int num..