Final answer:
The highest possible altitude at which Polaris can be observed is 90 degrees, which would be for someone located at the North Pole, making the correct option D) 90 degrees.
Step-by-step explanation:
The altitude at which Polaris, the North Star, can be observed in the night sky is directly related to the observer's latitude on Earth. At the North Pole, Polaris would be directly overhead, at the zenith, meaning it would have an altitude of 90 degrees.
This is because Polaris lies nearly at the north celestial pole, around which the entire sky appears to rotate. As you move southward from the North Pole, Polaris' altitude decreases correspondingly with your latitude. At the equator, Polaris would be on the horizon, at an altitude of 0 degrees, and further south, it would no longer be visible at all.
Thus, the highest possible altitude for Polaris from any position on Earth is 90 degrees, which corresponds to the altitude of the north celestial pole for someone standing precisely at the North Pole. This means that option D) 90 degrees is the correct answer.