4. The number of atoms of the elements in reactions a. Does not change but can be rearranged

b. Always changes.

c. Changes in some circumstances

d. Changes and doesn't get rearranged.

Where do the respiratory and circulatory systems meet? a. in the heart b. in the muscles c. in the lungs d. in the brain

What did not occur in the proterozoic eon a)the oxygen levels increase greatly in the atmosphere,b)the emergence of the eukarya , c)muti cella’s eukaryotic organisms began to diversify,d)anaerobic bacteria kept thriving with more oxygen

One of the reasons that stars are so large is because