When disposable income equals $800 billion, planned consumption expenditure equals $600 billion, and when disposable income equals $1,000 billion, planned consumption expenditure equals $760 billion. What is the marginal propensity to save? (当可支配收入等于8000亿美元时，计划消费支出等于6000亿美元，而可支配收入等于10亿美元时，计划消费支出为7,600亿美元。边际的储蓄倾向是什么？——中文由在线翻译而来，仅供参考)
选项：

A: 0.800.80
B: 0.640.64
C: 0.250.25
D: 0.200.20