/// <summary>
/// Enroll the student to an HSK level
/// </summary>
/// <param name="level">the HSK level</param>
public void Enroll(HskLevel level)
{
if (this._levels.Any(a => a == level))
{
throw new InvalidOperationException();
}
this._levels.Add(level);
}
public Example(NotEmptyText text, HskLevel level, Student author)
{
_text = text;
_level = level;
_author = author;
}
