Question

if a hot air balloon is seen rising above the top of a hill, what is the top of the hill called?

delta point

reference point

coordinate system

distance system

Explanation:

A reference point is a fixed point used for comparison to determine if an object is in motion. In this case, the top of the hill serves as a fixed point to observe the rising hot - air balloon. A delta point is not a standard term in this context. A coordinate system is a set of values that show an exact position. A distance system is not a relevant term here.

Answer:

reference point