Which of the following is an example of biological weathering?
a. plant roots growing through rock
b. water freezing in the cracks of rocks
c. oxygen reacting with the minerals in rock
d. rocks breaking from thermal expansion?

Afarmer who is grown corn for the past five years notices in the sixth year that the his harvest is significantly smaller, despite an increase in labor on the farm. the following year, the harvest continue to decline. which of the following explanations most plausibly accounts for the reduction in corn yield? a) soil degradation b) desalinization c) better irrigationd) terracing