public void RemoveQuestion()
{
using (UndoTransaction tx = new UndoTransaction(UndoManager))
{
StudyUnit.OnRemoveQuestion(SelectedQuestion);
SelectedQuestions.Remove(SelectedQuestion);
SelectedQuestionItem = null;
ConceptVM concept = SelectedConcept;
UpdateModel(false);
SelectedConcept = concept;
tx.Commit();
}
}