Sentence Correction

The gyrfalcon, an Arctic bird of prey, has survived a close brush with extinction; its numbers are now five times greater than when the use of DDT was sharply restricted in the early 1970's
A. extinction; its numbers are now five times greater than
B. extinction; its numbers are now five times more than
C. extinction, their numbers now fivefold what they were
D. extinction, now with fivefold the numbers they had
E. extinction, now with numbers five times greater than

Greatly influenced by the Protested missionary Samuel Kirkland, the Oneida was the only one of the five-nation Iroquois League who sided with the colonists during the American Revolution.
A.          was the only one of the five-nation Iroquois League who sided
B.          was alone of the five-nation Iroquois League when they sided
C.          alone among the five-nation Iroquois League sided
D.        were the only ones out of the five nations of Iroquois League in siding
E.          only of the five-nation Iroquois League had sided



please explain why the onida is plural but The gyrfalcon is singular

expert please explain singular plural with proper nouns in general