Where the commissioner has had to resort to investigations or the preparation of assets betterment statements or has otherwise had difficulty in assessing the tax ; or 局长须要进行调查或编制资产递增表，否则难以作出评税或
4.
Where the commissioner has had to resort to investigations or the preparation of assets betterment statements or has otherwise had difficulty in assessing the tax ; or 局长须要进行调查或编制资产递增表，否则难以作出评税；或
