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 distance
c) coordinate system
d) reference point

answer:

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 answer: 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.

answer:

explanation:   d reference point

wavelegth as in spectrum red oygbiv