The full-employment gross domestic product (GDP) is $1.3 trillion, and the actual gross domestic product is $1.2 trillion. The marginal propensity to consume (MPC) is 0.8. When inflation is ignored, what increase in government expenditures is necessary to produce full employment?
选项：

A: $100 billion.
B: $80 billion.
C: $20 billion.
D: $10 billion.