Which type of worksheets are not supported for sparklines according to the requirements?

The correct answer is crosstab worksheets. In the context of using sparklines, these visual tools are designed to provide a compact representation of data trends over time, typically used in scenarios where data is organized in a straightforward manner.

Crosstab worksheets, however, inherently involve multiple dimensions of data, presenting information in a grid format where both rows and columns represent different data points. This complexity makes it difficult for sparklines, which are meant to reflect simplified trends or patterns, to be applied effectively within such a multi-dimensional framework.

On the other hand, grouped worksheets, single-value worksheets, and bucketed worksheets can typically accommodate sparklines since they present data in a more linear or straightforward manner that aligns well with how sparklines are designed to function. Thus, while crosstab worksheets are incompatible with sparklines due to their complex structure, the other types of worksheets do not present the same challenges.