The correct format for naming a macro with multiple arguments is monthly_sales3. The square brackets indicate that the macro has arguments, and the number indicates how many arguments it has. The arguments are separated by commas when calling the macro, such as monthly_sales[region,salesperson,date].

https://docs.splunk.com/Documentation/Splunk/8.1.0/SearchReference/ConversionFunctions#tostring.28X.
2CY.29
The tostring function in the eval command converts a numeric value to a string value. It can take an optional second argument that specifies the format of the string value. Some of the possible formats are:
* hex: converts the numeric value to a hexadecimal string.
* commas: adds commas to separate thousands in the numeric value.
* duration: converts the numeric value to a human-readable duration string, such as "2h 3m 4s".
Therefore, the formats A, B, and D can be used with the tostring function.

The commands pivot and tstats both leverage data model summaries for faster search performance. The datamodel command itself is used to inspect or operate on data models. The transaction and stats commands do not directly access data model summaries.
Reference:
Splunk Power User Study Guide, Data Models and Pivot
Splunk Docs: tstats Command, pivot Command
"Both pivot and tstats are optimized to work with data model summaries for high-speed queries."