Why do simple animals, such as flatworms and sea stars, survive without special circulatory systems but more complex organisms, like reptiles and humans, cannot?

Flatworms get most of their oxygen through diffusion.

Explanation:

for e2020. the answer would be some directions from the mountain range so we can find mt. whitney. to locate which direction is north, you should use a   compass. this would not only find mt. whitney, but also becuase of this long paragraph you would get points because it's not like anyone actually reads your work becuase once they read the first sentence it sounds dumb enough to not read becuase i'm not good at answering this but the answer is compass for your benefit.

for e2020 ; -;