Ask questions in Batch file until valid response is made

How do you put the script in a 'loop' (re-ask the same question) when
an invalid response is made in the batch file?

For example, if you want either a "Y" or "N" response and someone
accidentally types a response of something else (like "T" or "M").

If an invalid selection is made, I'd like the batch file to ask the
question until a valid answer is made.

Any help is GREATLY appreciated!!!