The plural of the following
Subdivision
Maid of honour
Senior
Advocate
Grown up
Fountain
Pen
Appendix
Diagnosis
Nightmare
Scenario
Scavenger bird
Tenancy agreement
Subdivisions
Maids of honour
Seniors
Advocates
Grown ups
Fountains
Pens
Appendices
Diagnoses
Nightmares
Scenarios
Scavenger birds
Tenancy agreements
The plurals of the words you listed are as follows:
1. Subdivisions
2. Maids of honour
3. Seniors
4. Advocates
5. Grown-ups
6. Fountains
7. Pens
8. Appendices
9. Diagnoses
10. Nightmares
11. Scenarios
12. Scavenger birds
13. Tenancy agreements