Here are the sentences filled in with the appropriate forms of the words:

15. John is a stamp **collector**. He has a lot of rare and valuable stamps. (collect)
16. One third of children in the U.S. is **underweight** or obese. (weigh)
17. I have a **toothache**, so I must go to a dentist. (tooth)
18. Junk food is **unhealthy**, so we shouldn’t eat too much junk food. (health)
19. Blood **donors** give blood for use in hospitals. (donate)
20. They opened a shelter to provide housing for the **homeless**. (home)
21. His friends are all **artists** - they’re painters, musicians, and writers. (art)
22. He later became a famous jazz **musician** playing saxophone. (music)
23. The problems seemed so small and **unimportant**. (important)
24. The soup had a very **salty** taste. (salt)
25. She covered the cake with a **mixture** of sugar and whites of eggs. (mix)
26. Most children enjoy **frying** chicken and French fries. (fry)

Feel free to ask if you need anything else!