English plural nouns of foreign origin

1. How many are there? (stratum)
2. Four have been presented so far. (hypothesis)
3. I am going to sell these two of stamps. (series)
4. For the first time these were noticed two years ago. (phenomenon)
5. Too many at the same time many lead to chaos. (stimulus)
6. All the is question were caused by inefficient management. (crisis)
7. He has written many excellent for us. (analysis)
8. Some can be found in the zoological gardens only. (species)
9. The collected by you are very important for us. (datum)
10. Are these two radii equal? (radius)
11. These were made by my uncle Sam when he was a prisoner of war. (die)
12. We have dealt with these for a long time. (phenomenon)
13. can be seen only through a microscope. (bacterium)
14. All these are inadequate. (analysis)
15. Have you ever heard of food produced from . (alga)