Explanation:

Both (a) and (b) is correct

By relying on the judgment of this Court in Confederation of Ex. Servicemen Associations v. Union of India  , the learned Additional Solicitor General argued that the classification between defence personnel and other than defence personnel is reasonable and valid. It was further contended on behalf of the Appellants that the conditions of service of Commissioned Officers in the Army and civilian Chief Engineers are entirely different. Commissioned Officers are liable to be posted anywhere in the country including hard field areas such as Jammu and Kashmir and the North East, unlike civilian engineers who do not have an all-India liability. Similarly, Classification between resident and foreigner is valid.

Hence option 3rd is correct.