Gross domestic product includes consumption, net exports, and

a exports, imports
b personal income taxes, public goods
c investments, government expenses

GDP is a measure for the the value of economic activity within a country and counts both  goods and services.

Gross Domestic Product (GDP) includes consumption, net exports, investments and government expenses. Correct C GDP does not include household production and illegal markets.GDP  is the sum of consumption (C), investment (I), government spending (G) and net exports (X – M).

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.