Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

The sustainable growth rate is best estimated as:
Option A:the weighted average of capital and labor growth rates.
Option B:growth in the labor force plus growth of labor productivity.
Option C:growth in total factor productivity plus growth in the capital-to-labor ratio.

Answer: B