A very sensitive spring balance was used to determine the weight of an object at the north pole. When the same spring balance was used to measure the weight of the same object at the equator, it was found to reduce. The explanation for this observation is that

• A.it is very hot at the equator
• B.the spring balance has expanded
• C.the acceleration of free fall due to gravity varies with location
• D.the mass of the body is reduced