It looks like you're asking to fill in the comparative forms of the adjectives you've listed. Here’s how to place them in the correct form based on the rules you provided:

1. big → bigger (double letter rule for short adjectives)
2. fast → faster (add -er)
3. fat → fatter (double t and add -er)
4. happy → happier (y changes to i and add -er)
5. hard → harder (add -er)
6. heavy → heavier (y changes to i and add -er)
7. hot → hotter (double letter rule for short adjectives)
8. long → longer (add -er)
9. short → shorter (add -er)
10. thin → thinner (double letter rule for short adjectives)
11. tidy → tidier (y changes to i and add -er)
12. ugly → uglier (y changes to i and add -er)

If you need further explanations or examples, feel free to ask!