Using the Rule of 70,a Sustained 3 Percent Per Year

Using the rule of 70,a sustained 3 percent per year real GDP growth rate will

A) last for 70 years.
B) double the current level of real GDP in about 23 years.
C) double the current level of real GDP in about 210 years.
D) double the current level of real GDP in about 70 years.
E) double the current level of real GDP in about 40 years.