Keyword dictionaries can be created either from a text file or from csv file.
Note:
There are several versions of this question in the exam. The question has two possible correct answers:
a CSV file that contains words separated by commas
a text file that has one word on each line
Other incorrect answer options you may see on the exam include the following:
a TSV file that contains words separated by tabs
a DOCX file that has one word on each line
an XML file that contains a keyword tag for each word
Reference:
https://docs.microsoft.com/en-us/microsoft-365/compliance/create-a-keyword-dictionary?view=o365-worldwide