A system of millions or billions of stars together with gas and dust, held together by gravitational attraction
I’m guessing a coral reef becuase of all the different species of fish or a tropical rainforest if you look up what ecosystem contains the greatest species diversity you’ll find the answer :)
D. City and U.S. Government, but I’m not sure what the context is though.
A. When new evidence that challenges old ideas is presented.
Think about the other choices, they do not make any sense. You cannot change your ideas just because people want something to be a certain way. And you have to change your idea if you're proven wrong.