Which of the following situations would most likely require using the inverse-square expression for gravitational force rather than assuming a constant acceleration g=9.8m/s2?
a) A diver jumps from a 10m platform into a pool.
b) An elevator travels to the top of a 200m skyscraper.
c) A weather balloon ascends from sea level to 30km altitude.
d) A mountaineer climbs 1.0km from base camp to a summit.