the only reason i am wasting one of the two answers your post is allowed to get is because its been 3 hours and no one has answered yet.
Where do you go to school? I think it is very coincidental that you have the exact same question i do, and you had the question exactly when I got the question...about 3 hours ago. Now it IS a curriculum so its not that weird, but by any chance are you in K12? 8th grade?
The correct answer is indicator species.
Factories, cars and cigoretes.
All of these things are polluting the air cuasing it to heat up more which is cuasing global warming
I think the third one is the answer
I think the organisms are compared to each other.