Air pollution is caused by  a. the sun.  b. heavy rainfall.  c. natural events and human activities.  d. human activities but not natural events.

It's a tie for me between C. and D. but I am going to say D. I hope this is the right answer for you.

I would say your answer is D) human activities but not natural events.

because we cause it by burning coal, gases from our cars, or harming the enviroment it isnt caused by rainfall or sun.

sorry if im wrong

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.