Cover crops are not a separate question anymore but are part of C input added to a soil. Have a look at the info button text in the tool, you will see a helpful soil carbon decision tree (can also see attached to this article). If you started using cover crops and they stay on ground for more than 6 months, they would change your C input regime from a lower to a higher category. Again, the same text/decision tree will help you to choose your starting category.