The rule of 70 states that:
A.the average lifespan of a developed nation should be at least 70 years.
B.everyone should retire by age 70.
C.the number of years for a variable to double equals 70 divided by its annual growth rate.
D.Social Security benefits should increase when people reach 70.
E.a nation cannot be considered developed unless at least 70% of the population is literate.