Upon the hearing of an exclusion petition the board shall order that the petition be denied:
(a) Entirely when no evidence in support of the petition is introduced.
(b) As to any land described in the petition as to which the evidence introduced fails to sustain the petition.
(c) As to any land described in the petition which the board deems it not for the best interests of the district to exclude, except when the board judges that the land will not be benefited by the operations of the district.