What requirement must be met for calculating summarization in hierarchy columns?

The correct choice indicates that for calculating summarization in hierarchy columns, it is essential that the worksheet has only one dimension column. This is important because hierarchy columns operate on a single dimension to facilitate proper aggregation and summarization of data. If multiple dimension columns were present, it could lead to confusion and errors in how the data is interpreted and summarized, as the application would struggle to discern how to correctly aggregate the multi-dimensional data.

A single dimension column simplifies the process by providing a clear hierarchical structure, allowing for effective summarization of numerical data associated with that specific dimension. This focus helps maintain clarity in data analysis and ensures that summaries for reporting or further analysis are consistent and accurate.