Which of the following best describes the structure used for storing data in a Cube?

The correct choice accurately describes the structure used for storing data in a Cube by emphasizing the organization of data into indexed rows and columns within tables. In the context of a Cube, this structure allows for efficient retrieval and analytical processing of multidimensional data. Cubes are designed to support complex queries involving various dimensions and measures, and the indexed approach facilitates quick access to specific data points.

This structure is particularly beneficial for analytical applications where users need to quickly slice and dice through large sets of data, making it possible to analyze data across different perspectives and time frames. The use of rows and columns also mirrors traditional database practices, but it's specifically tailored to optimize the performance and usability of multidimensional data analysis.

Other structures mentioned do not encapsulate the fundamental organization of a Cube as effectively. For example, a hierarchical structure involves a tree-like arrangement which may not fit the multidimensional analysis requirements as intuitively as an indexed row-column approach. Similarly, a flat file structure lacks the complexities and efficiencies needed, while a relational database structure, although useful, operates on a different multipurpose transactional paradigm rather than specifically tailored for multidimensional analysis like cubes.