List field options from another section
The CMS doesn't support that directly, but you can do it with custom MySQL code. It's a bit more advanced but give this a try:
SELECT num, CONCAT(title, ': ', content)
FROM `<?php echo $TABLE_PREFIX ?>section_b`
ORDER BY title
The first field is what is stored in the database, the second is what is shown to the user. The reason we usually want to store a record number in the database is so if the title or content changes we can still find it by record number.
The MySQL CONCAT function joins multiple values together.
Hope that helps!