The rule of 70 tells us that:
A.
it takes most countries 70 years to increase real GDP growth.
B.
the number of years it takes for a variable to double is equal to 70 divided by the annual growth rate of the variable.
C.
the number of years for real GDP per capita to double is the current growth rate plus 70.
D.
only 70 countries can have real GDP growth at any given time.