Which of the following most accurately represent the meaning of the term 'balance of payment'?O$.$ a$.$ The difference, over a period of time, between the total flow of money coming into a country and the total flow of money going outO b$.$ The difference, over a period of time, between the total flow of imports into a country and the total flow of exportsO c$.$ The difference, over a period of time, between the flow of money, goods and services coming into a country and the total flow of money going outO d$.$ The difference, over a period of time, between the total of income and expenditure of a country