Answer:
sense of self-interest.
Step-by-step explanation:
The given quote is taken from the book titled 'The Wealth of Nation' written by Adam Smith. The book is about the free-market economics and it's pros and cons to the economy.
In the given quote, Adam Smith is talking about that it is sense of self-interest that motivates people to seek high-paying jobs rather than the desire of interest of society. He asserts that people are exerting themselves to seek high-paying jobs for his own advantage than advantage to the society.
Therefore, option D is correct.