On which of the following ground can the Central Government supersede the Board?

Section 17 of SEBI Act - (1) If at any time the Central Government is of opinion— (a) that on account of grave emergency, the Board is unable to discharge the functions and duties imposed on it by or under the provisions of this Act; or (b) that the Board has persistently made default in complying with any direction issued by the Central Government under this Act or in the discharge of the functions and duties imposed on it by or under the provisions of this Act and as a result of such default the financial position of the Board or the administration of the Board has deteriorated; or (c) that circumstances exist which render it necessary in the public interest so to do, the Central Government may, by notification, supersede the Board for such period, not exceeding six months, as may be specified in the notification.