Here is the full solution for CraftConnections Day 4. Each group is shown with its difficulty colour and a redundant shape, so it stays readable if you are colour blind.
Classic — Day 4
● Axes Wooden Axe · Stone Axe · Diamond Axe · Iron Axe
▲ Wool Yellow Wool · Green Wool · Light Blue Wool · Brown Wool
◆ Blocks that hold your stuff Hopper · Smoker · Blast Furnace · Barrel
★ Crafted with string Crossbow · Scaffolding · Loom · Fishing Rod