If you see that a hot air balloon is rising above the top of a hill, what is the top of the hill called? delta pointdistance systemcoordinate systemreference 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. The correct option among all the options that are given in the question is the fourth option or the last option. I hope that this is the answer that you were looking for and the answer has actually come to your desired help.

Answer) by studying proton collisions hope this : )