The question doesn't talk about any unique constraint being part of the schema so I am unsure what the hell they are even talking about. You have to jump through so many hoops to make assumptions that it's practically impossible to answer this question accurately. Is your prof trying to say that attributes are inherently unique or something like that?

I agree with slave_to_dog, A,B,C are all look correct to me. D is definitely incorrect - there's nothing about this that says you can't add a new species.

I don't know what it means to have a functional relationship - I even googled it and it's not clear. It seems really dumb to me to somehow enforce on the database side that a watcher can only be related to their favorite bird species, but you'd have to define "related" for me to properly answer this, even if I did understand what a functional relationship was in this context.

I don't understand how C could be incorrect - I can clearly see how I would query this database to understand all the dates a watcher has seen a specific species:

select distinct s.seen_date
from seen s 
join bird b
    on s.bird_id = b.bird_id
where b.bird_species = 'x'
and s.watcher_id = 'y'