Question

select the word that means performing tasks without being wasteful.
the sloth is one of the worlds least active animals. it spends most of its time hanging in trees and sleeping. but some people have wondered if sloths really deserve their reputation for laziness. with all their hanging around, maybe sloths are just being efficient. sloths eat mostly leaves, which provide very little energy. therefore, sloths bodies may have adapted to allow them to save energy by moving slowly.

Explanation:

The key - phrase is "performing tasks without being wasteful". The concept of using resources (in this case, energy) effectively without waste is related to the word "efficient". The text about sloths also mentions them being efficient in terms of energy - use.

Answer:

efficient