A country is said to be in balance-of-trade equilibrium when _____.
选项：

A: it has the potential to produce all goods that its residents want without engaging in foreign trade
B: the income its residents earn from exports is equal to the money its residents pay for imports
C: the country import all goods that its residents want by engaging in foreign trade
D: it has the potential to balance the production and procurement of the basic amenities that it needs