If you see that a hot-air balloon is rising above the top of a hill, what is the top of the hill called? a. delta point b. distance system c. coordinate system d. reference point

If you see that a hot-air balloon is rising above the top of a hill,  the top of the hill is  called the reference point. Correct D The reference point is a point (object, place) used for comparison to determine if something is in motion,  assuming that the reference point is stationary, or not moving.

the inner core.

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klicker

a sonic boom is a loud boom that breaks the sound barrier

explanation: