Answer: 0.69 m/ mile.
Explanation:
The altitude gradient between two cities X and Y = 
Given: Two cities are separated by 200 miles.
City X has an altitude of 122 meters.
City Y has an altitude of 260 meters.
The altitude gradient between two cities X and Y =

Hence, the altitude gradient between the two cites = 0.69 m/ mile.
Example of selective breeding: Cows that produce lots of milk. Selective breeding to create more useful varieties of animals and plants is a form of biotechnology that human beings have used for thousands of years. Biotechnology includes any use of science or technology to alter the characteristics of a particular breed or animal.
sand dunes
because it is and sand dunes get deposited
Chage identity of a substance
Answer: option D
The sodium potassium ion exchange move sodium and potassium in opposite direction in electrochemical gradients.
Explanation:
The sodium potassium pump is found in many animals plasma membranes and its moves the sodium and potassium ion in opposite direction across the plasma membrane with the hydrolysis of ATP(adenosine triphosphate) to supply the needed energy. It is an active transport process.