Question

the power of water
if youve ever seen a river chuckling as it rushes by, like its carrying feathers instead of boulders, you know how powerful moving water is. over the years, people have learned how to harness the power of water not only for recreation, but also for energy. hydroelectricity is made by taking the energy of running water and changing it into a form of energy that we can use. hydroelectric plants create nearly one - fifth of the worlds electricity. this makes the enormous power of water one of the most important energy sources on earth.
on page 1, what is the most likely reason the author chose the word harness?
to give the reader a sense of how difficult it is to make power from water
to create an image for the reader that humans are permanently tied to water
to show the reader that people have the ability to master elements such as water
to help the reader picture the control that humans have developed over water

Explanation:

The word "harness" means to control and use a natural force for a purpose. The text explains humans use water's power for energy (hydroelectricity), so the word emphasizes human control over water's power. The other options don't fit: the text doesn't focus on difficulty of making power, permanent ties to water, or mastering elements generally.

Answer:

to help the reader picture the control that humans have developed over water