For small open economy, assume that the marginal propensity to import is 0.3, and that interest rates, exchange rates, and the price level are all constant. If an increase of $10 billion in government spending results in an increase of $6 billion in imports, then:

A.real GDP increases by $4 billion.

B.the spending multiplier is 2.

C.taxes increase by $10 billion.

D.real domestic investment decreases by $4 billion.

正确答案：real GDP increases by $4 billion.