public async Task Book(IBook <string> activity)
{
activity.book("HOTEL");
activity.BookingComplete();
await Task.Delay(1000);
activity.book("HOSPITAL");
activity.BookingComplete();
await Task.Delay(1000);
activity.book("RESTAURANT");
activity.BookingComplete();
await Task.Delay(1000);
activity.book("THEATRE");
activity.BookingComplete();
await Task.Delay(1000);
//return Task.CompletedTask;
}