Which one of the following is not a natural cause of climatic change
a. volcanic
b. earth's tilt
c. solar activity
d. human activity

Which factor contributed to the rise of african empires such as ghana and mali?

Which of the following is a problem in the health care system of the united states? a. too many doctors in rural areas b. too many doctors who are general practitioners c. fraud d. costs that are too low

In e. c. tolman's experiment, some rats were trained to run through mazes for standard food goals, while other rats were allowed to explore the mazes for 10 days without food goals or other rewards. later, when food rewards were placed in a box at the far end of the maze, the previously unrewarded rats reached the food box as quickly as the rewarded rats after only one or two trials. this experiment demonstrated that the rats had the ability to form of their surroundings.