Empirical evidence from 1960 to 2010 shows that convergence in economic growth is occurring in which of the following cases?

a. All low-income countries are catching up to all high-income countries.
b. Low-income industrial countries are catching up to high-income developing countries.
c. Low-income developing countries are catching up to high-income industrial countries.
d. Low-income industrial countries are catching up to high-income industrial countries.