// Variable queryID could be declared by using 
// System.Collections.Generic.IEnumerable‹string›
// instead of var.
var queryID =
    from student in students
    where student.ID > 111
    select student.LastName;

// Variable str could be declared by using var instead of string.     
foreach (string str in queryID)
{
    Console.WriteLine("Last name: {0}", str);
}