假定投资和储蓄是由下列等式所确定的：I=50一r．S=4r。 a．如果经济是封闭的。那么，利率、储蓄、投

资和经常项目的均衡水平各是多少？ b．如果该国是一个小国开放经济，且国际利率为8％，那么，a的答案会作何变化？如果利率升至12％。又会发生什么情况？ c．如果投资函数变为I=70一r。那么a和b的答案有什么变化？ Assume that investment and saving are determined by the following equations：I=50-r；and S=4r． a．If the economy is closed，what are the equilibrium levels of the interest rate，savings，investment，and the current account？ b．How would your answer to(a)change if the country is a small open economy and the international interest rate is 8 percent？What would happen if the interest rate rises to 12 percent？ c．How would your answer8 to(a)and(b)change if the investment function becomes I=70一r？