In a functional structure, the organization is divided into smaller groups based on specialized functional areas such as marketing, finance, operations, etc. Each functional unit is managed independently and is responsible for its area of operation. In the case of Sunita Travels, the company has been organized by function: reservations, hotel bookings, online queries, and payment handling. Each of these functions operates as a separate department, which indicates the use of a functional structure. This structure promotes operational efficiency, enhances specialization, and ensures better supervision within departments.
Final Answer: (A) Functional structure