Ahorizontal line on a velocity/time graph shows acceleration.

Zero acceleration

Explanation:

In a velocity-time graph, the gradient of the line describes how the acceleration varies.When the gradient is positive, it means we have a line that is upward sloping thus the accelaration is positive.When we have a negative gradient, it means the line is downward sloping thus the accelaration is negative.When the gradient is zero, there is no slope, thus the accelaration is zero, the case of a horizontal line.

there was no answer choices but i think its representative

as we know our atmosphere or air have different levels. every level has other gasses, and every gas has another permeability. when the light comes from lower permeability to higher permeability, it changes its direction. so that means that when the light comes from the moon to the earth, it changes it's direction many more times. it basically means that the shape of the light part of the moon is changed on the earth.

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