Researchers compared the changes in the bones of people who have lived in Europe over the past 33,000 years and found that from the Middle Stone Age 10,000 years ago to the Roman Empire 2000 years ago, the strength of both human leg bones continued to decline, but compared with the strength of the upper arm bones not related to running and walking remained stable. It was also during this period that agriculture began to rise and humans gradually shifted to a settled lifestyle. The rise of agriculture caused the bones of modern people to become lighter, but the strength of the two types of leg bones thereafter With little change, the researchers concluded that the effects of mechanization and urbanization on bone strength were not significant. Which of the following is most likely the hypothesis that the researchers made their conclusions? ['Over the past 33,000 years, the overall weight of humans has changed little.', 'No significant changes in human lifestyles from 33,000 years ago to 10,000 years.', 'Mechanization and urbanization occur after the rise of agriculture.', "Lightening of a person's bones causes a decrease in their bone strength."]