Missing letters

Which letter/letters is missing? Fill in all the gaps, then press "Check" to check your answers.

1. ELEPANT
2. CT
3. ONKE
4. EBRA
5. LON
6. FO
7. TUTL
8. BR
9. DO
10. CO
11. ORE
12. BUNN
13. SHP
14. CROCDLE
15. DONKE
16. MUSE
17. ROG
18. GIRAE