The correct answer is C) the difference between the heights of high and low tide. The range of tide refers to the vertical distance between the high and low tide levels at a given location. This is the difference in water height between the highest and lowest points of the tide cycle. Answer C correctly identifies this as the key definition of the range of tide. The other answer choices are incorrect because they do not accurately describe the definition of the range of tide. The maximum depth of water (A), the distance the tide moves out (B), and the duration between high and low tide (D) are related concepts, but they do not directly capture the definition of the range or difference in tide heights.