Refer to the Diagram $\left( \mathrm { C } + I _ { g } + X _ { n 2 } \right)$

Refer to the diagram. The change in aggregate expenditures as shown from $\left( \mathrm { C } + I _ { g } + X _ { n 2 } \right)$ to $\left( C + I _ { g } + X _ { n 1 } \right)$ might be caused by

A) an appreciation of this nation's currency relative to the currencies of its trading partners.
B) a depreciation of this nation's currency relative to the currencies of its trading partners.
C) a decrease in this nation's price level relative to price levels abroad.
D) a rightward shift in this nation's 45-degree line.