Which type of document typically contains a significant amount of numbers and should be excluded from the training set?

The choice indicating that Excel files with mostly numbers should be excluded from the training set is based on the nature of the data typically found in those files. Excel files are often used for quantitative data analysis, containing extensive datasets, numerical calculations, and statistical information. These types of documents generally do not provide the qualitative insights or contextual information that are beneficial for training models focused on language comprehension or text analysis.

In contrast, Word documents, PDF files, and PowerPoint presentations usually include prose, descriptions, and narrative content that can enrich a training set aimed at understanding human language and contexts. Therefore, Excel files, which primarily consist of numerical data, are typically less suited for training purposes, as they may not contribute effectively to language-driven machine learning tasks.