If each level in a food chain typically loses 90 percent of the
energy it takes in, and the producer
level uses 1000 kcal of energy, how
much of that energy is left after the
third trophic level?

Because the earth is not round ,but it may seem round when viewed from ,our planet but true some points earth is not round was an oblate spheroid -a square that it squashed as globe however is not even a perfect oblate spheroid.in fact isaac newton's first proposed that earth was not perfectly round but it was an oblate spheroid instead.that mean a square that is squashed as its poles and swollen at the

Cbecause it is the only one describing a habitat

Digestion because it removes waste

Iwould say overuse ( but not 100% sure ) in the u.s. we tend to overuse water by leaving it running, throwing it away, taking long showers, etc.