Cannot be gained or lost during a reaction, only transformed.

a. air
b. matter
c. electricity
d. reactants

2. if scientists identify an animal with bilateral symmetry and no segmentation, which phylum can it definitely not belong to? a. roundworms b. annelids c. mollusks d. flatworms

Why are scientists concerned about the depletion of the ozone levels in the stratosphere?

How do you suppose living conditions differ between the country furthest along in the demographic transition compared to the country earliest in the transition? how would living conditions in these two countries affect both birth and death rates?