Adam smith argued that people were motivated to engage in economic activity by

Adam smith argued that people were motivated to engage in economic activity by "self-interest".

Self-interest alludes to an attention on the necessities or wants (interests) of the self. Various philosophical, mental, and monetary speculations inspect the part of self-enthusiasm for inspiring human activity. Adam Smith, the father of  modern economics, broadly clarified that it is conceivable to accomplish the best monetary advantage for all notwithstanding when, and in certainty since, people tend to keep their best interests in mind.

It’s either d or b ! but it might be b