The period at high or low tide during which there is no change in the height of the water is called the （）.

A.tide is falling from high water to low water
B.tide is rising from low water to high water
C.tide is reaching to a highest level
D.tide is reaching to a lowest level

A.depth of water at a specific time due to tidal effect
B.difference between the depth of the water and the area's tidal datum
C.difference between the depth of the water and the high water tidal level
D.difference between the depth of the water at high tide and the depth of the water at low tide

A. the angle between the horizontal and the line of sight to the visible horizon
B. index error
C. parallax
D. terrestrial refraction