ex3.cs

 public static WeeklyActivityRecorder WithActivities(this WeeklyActivityRecorder recorder, params   Expression<Func<DayOfWeek, string>>[] activities)
 {
  foreach( var activity in activities )
  {
     LambdaExpression expression = activity;
     ConstantExpression activity= expression.Body as ConstantExpression;
     DayOfWeek day =  expression.Parameters[0];
     recorder.AddActivity(new Activity {DayOfWeek = day , Activity = activity});
  }
 return recorder ;
}