i have a questión, another more. If "nombre" is number why not "nombreux" is numbers? it seems logic.
Nombreux=Numerous (masculine) Nombreuse=Numerous (feminine singular) Nombreuses=Numerous (feminine plural)
In the excersice before this one, an example said to use "Ce sont" whenever it could be substituted by "Ils sont" ... so what do we do?
"Ce sont" (plural version of "c'est") is used if it is followed by a plural noun ("ce sont des oiseaux"); "ils/elles sont" if there isn't any noun following, just an adjective (like in this exercise).
Sometimes even if there is no noun, we do use "c'est", mostly in an exclamation: "c'est beau !" (instead of "il est beau !")
It means the same thing conceptually but is not a direct translation, which is what you are supposed to do for these exercises.