After meeting the tributes of the Temple of Water, cleaning up the seabed garbage, upgrading the museum and donating more than 100 exhibits, the town's rating will be upgraded to C level, and Sam's Supermarket will provide a variety of new seeds, including winter tribute seeds.
Many people will be stuck at C in the first year of town and cannot be upgraded to D (need to enter the innermost room of the community center to view the rating). This has resulted in winter tribute seeds not being purchased in the store.
To upgrade to level C, the following four conditions must be met:
Complete all tributes from the Temple of Water, except for winter tributes.
Clean up most of the seabed garbage, at least to close to the Mermaid Palace.
Upgrade the museum and donate more than 100 exhibits (no counting in the game, and you need to count them yourself).
You cannot upgrade to Level C in the first year, but after meeting the above three conditions, you will automatically upgrade in the second year (to be confirmed).
Upgrading to C-Class, Sam's Supermarket will offer a variety of new seeds, including winter tribute seeds.