Answer:
The correct answer is the last option: increasing investment in capital that boosts worker productivity.
Step-by-step explanation:
To begin with, the supply-side economy is a type of economic ideology that focuses in the idea of increasing the supply in the economy in order to obtain better production and in that way better results in the economy due to the higher rate of employment that will be caused for those motives and furthermore due to the higher expenditure that will be caused as well.
Secondly, the reason why increasing investment in capital that boosts worker productivity is the policy that supply-side economists believe is the best for increasing the standard of living is due to the fact that in that way the production will increase because of that investment that made the workers complete their jobs much better.