It can be a data source, or a database, an excel sheet. or access database. However, it must be well-formatted and hence organized. filtering of data is not necessary, as well as it is not any barrier to the number of the set of data, or the data being sorted. Unsorted data is also fine, and multiple set of data is also fine. It must be known that a data source can be formed from multiple sets of data through the query. And the resultant data source can be used by the mail merge. However, the data source must be a collection of organized data. Hence, A is the correct answer.
