According to the passage, which of the following is true regarding environmental changes 4,000 years ago? A. No localized increases in grass pollen were caused by agricultural development. B. Increases in grass pollen were at least sometimes a reflection of an increase in aridity. C. Wholesale ecosystem changes probably resulted from agricultural development. D. Any small-scale changes occurring then would not be detectable now. E. Environmental change helped induce the adoption of agricultural technologies.