Hi!
The correct option would be A. There's lower biodiversity among birds
Biodiversity refers to the variety of organisms (species) that inhabit a particular place, such as in our case different species of birds.
From the graph we can see that over time, the bird species are declining. From roughly 1700 bird species, the number has fallen to about 200 bird species by the middle of the fourth year.
Hence, we can deduce, and it would be accurate to say, that there is a relatively lower biodiversity amongst the birds with regard to that in the beginning.
Option B is incorrect because if the birds had a higher reproductive rate, they would be able to make up for the loss of bird species from the habitat. From the graph, we can assume that there's a moderately low reproductive rate among the birds.
Option C is incorrect because we do not know the affect of this pollution on the producers (photosynthesizing plant lifeforms). It may be possible that they might be declining, but we cannot conclude that solely from the graph.
Hope this helps!