Answer:
In fact, the exercise is about changing the adjective into its adverb form and vice-versa.
Across:
4. excitedly (adv)
7. loudly (adv)
10. quietly (adv)
11. hungry(adj)
13. wisely (adv)
15. easily (adv)
18. wrong(adj)
20. rude(adj)
21. rarely (adv)
Down:
1. eagerly (adv)
2. carefully (adv)
5. calm(adj)
6. extremely (adv)
8. badly (adv)
9. hungrily (adv)
12. honestly (adv)
14. lazy (adj)
16. slow (adj)
17. angry (adj)
19. well (adv)
Explanation:
Usually, when we transform the adjective to the adverb form, we add "ly" at the end of the adjective.
Example: Excited -> Excitedly
However, if the adjective ends with letter "y", you must change "y" to "i" and then add "ly" at the end.
Example: hungry -> hungri + ly = hungrily; angry -> angrily
In addition, there are several special adjectives that their adverb forms are totally different from the above rule. A special adjective can be found in the exercise is:
1. good (adjective) - its adverb form is "well" (adverb)