LINQ query to comma separated string with "and" at end
var names = unique.Select(p => p.FirstName + " " + p.LastName).ToArray();
string result = string.Join( ", ", names.Take(names.Length - 1))
+ (names.Length <= 1 ?"":" and ")
+ names.LastOrDefault();
// just a comma separates list
var names = t.Students.Select(p => p.CompetitionEventStudent.Student.LastName).ToArray();
string teammates = string.Join(", ", names);