Which of the following is true of the gravity model?
A.
The gravity model states that the trade flows between two countries is independent of the geographical distance between them.
B.
The gravity model emphasizes on the role of the government to generate adequate gains from trade.
C.
The gravity model states that trade flows between a developing and a developed nation is usually unidirectional.
D.
The gravity model states that the trade flows between two countries is directly proportional to their GDP.