The correct answer is A) the powder is an unnatural substance.
The statement that best explains how the phrase “white granular powder” supports the author’s purpose of calling attention to the environment is "the powder is an unnatural substance."
Unfortunately, you did not include further context, excerpt, or references. But it seems you are talking about an excerpt of the book "Silent Spring," written by American author Rachel Carson.
Rachel Carson's book, “Silent Spring”, shocked the world in 1962 because it created a consciousness of the use of DDT and the terrible consequences it had on human diseases. Nobody before Carson’s conclusions had thought on this serious issue.
The book was the originator of environmental and ecological movements that targeted the use of chemicals and the support for nature and life. “Silent Spring” impacted the world after knowing the dangers of toxic chemical pollutants in the air.
