Which of the following is not true concerning the energy harnessed by humans throughout history?
a. early hominids harnessed the least energy, just that of their own bodies.
b. fire let humans increase their energy use tenfold.
c. neolithic farmers were able to harness the energy of animals.
d. modern humans use more than a hundred times the energy of early humans.

The correct answer is option b. "Fire let humans increase their energy use tenfold". During the history of energy harnessed by humans the use of fire represented an achievement for warming during night and cooking food. However, its use did not represented an increase in energy use tenfold, as energy harnessed in food is not ten times higher if it is cooked with fire in comparison with not cooked with fire.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.