Final answer:
The statement is true. In the sort stage, existing fields or columns are used to determine the sorting criteria.
Step-by-step explanation:
T or F: You can only use existing fields in the sort stage.
The statement is true. In computer programming, particularly in relational databases, the sort stage is used to arrange data in a specific order. During this stage, the existing fields or columns are used to determine the sorting criteria. For example, if you have a table of students with columns like 'name', 'age', and 'grade', you can sort the data based on any of these columns.