Under Section 3 of the Airports Authority of India Act, 1994, which of the following must invariably be an ex officio member of the Authority?

Section 3(3)(b) provides that the Authority shall consist of, among others, the Director General of Civil Aviation, or an officer not below the rank of Deputy Director General of Civil Aviation, appointed by the Central Government as an ex officio member. Besides this member, the Authority comprises a Chairperson appointed under clause (a), and not less than eight and not more than fourteen other members appointed under clause (c), serving whole-time or part-time. Section 3(5) requires the Chairperson and clause (c) members to have special knowledge of air transport, other transport services, industry, commerce, finance, or administration, and to include persons capable of representing workers' and consumers' organisations - balancing regulatory, technical and stakeholder representation.