What is the single most important source of u. S. Economic growth?

Increase in Labour productivity

Explanation:

The hourly output of a country's economy is called labour productivity, it informs about the real gross domestic product produced by the labour in an hour.

Human Capital, Physical capital and new technology are the factors that affect the growth in labour productivity. Government and Businesses can increase the labour productivity by creating incentives.

Tools, equipment and facilities available for worker for producing goods is physical capital, new technologies such a s automation and assembly lines and the Human capital such as the specialisation of the workforce and education levels directly affect the productivity of the labour force.