The correct answer is employees. The idea is that employees keep the business running - they watch the stocks, deal with the customers, order supplies, keep track of profits and where they’re being spent, etc.
However, a lot of companies don’t follow this up by following the newest employees properly or by making older employees feel as though they’re useless by paying the newer employees more.
A business’s most important resource should be their employees. Without the employees, nothing would get done (unless the process has been automated, but those will back up). So, business owners find ways to value their employees while still getting the best bang for their buck. Sometimes it works, and sometimes it doesn’t.