(a) direct a housing authority to offer for sale under section 90 of the Principal Act a house of the authority of such class as may be specified in the direction,
(b) direct a housing authority not to sell a house of the authority of such class as may be specified in the direction,
(c) revoke or amend a direction under this section.
(2) Section 90 of the Principal Act shall apply, and be deemed always to have applied, to a building consisting of a house and a shop, together with any outoffice, yard, garden or other land appurtenant thereto or usually enjoyed therewith.
