From the original task to reading for information.
The last sentence certainly sums up the rest of the contents. I think you ought to choose the second answer.
The answer is: To emphasize the horror of what has happened.
Silent Spring is an environmental book written by Rachel Carson in 1962. She focused her attention on environmental problems specially the ones caused by synthetic pesticides. Carlson wrote the book after researching to make American people aware of the problems they were facing. Even though it had opposition from the chemical companies, it brought about important changes.