When selecting hidden columns for a chart, what must also be included?

When selecting hidden columns for a chart, it is essential to include at least one non-hidden column. This requirement is rooted in the way charts are structured and rendered. A chart needs a reference point in terms of visible data to provide context and meaning to any hidden data being displayed. If only hidden columns are selected, the chart would lack the necessary data to visualize relationships, trends, or comparisons effectively, which could lead to confusion or misinterpretation of the information being presented.

Including at least one non-hidden column ensures that there is a baseline or a reference series for the chart, enabling the viewer to understand how the hidden data fits into the overall picture. This combination helps create a coherent visual representation of the data.

The other options provided do not meet the fundamental requirements for creating a meaningful chart. While hidden columns can be included for various analytical purposes, their effectiveness is significantly diminished without the presence of at least one visible counterpart.