From "The Roots of Organic Farming"

What is the main idea of this text?
A. Instead of natural methods and tools, untested synthetic chemicals are being used by farmers to increase crop yields and profits.
B. The modern practice of organic farming developed primarily in reaction to concerns over the negative effects of synthetic chemical fertilizers and pesticides.
C. Organic farming offers people an alternative source of food that does not contain chemical fertilizers, pesticides, or genetically modified products.
D. Throughout the 20th century, scientists and others have challenged the safety and effectiveness of synthetic chemicals used in farming.