Supernova29
In his book, Wealth of Nations, Adam Smith, generally regarded as the father of economics, defines 'economics' as the 'science of wealth'.
A. In his book, Wealth of Nations, Adam Smith, generally regarded as the father of economics, defines
B. Adam Smith, generally considered to be the father of economics, inWealth of Nations, defines
C. In Wealth of Nations, Adam Smith, generally regarded to be the father of economics, defines
D. Adam Smith, generally regarded the father of economics, in his book, Wealth of Nations, defines
E. The father of economics, Adam Smith, defines 'economics', in his book Wealth of Nations as

Excellent job by TirthankarP.
However, I have another way to solve this question, because some time I can't remember correct idioms.
The idea of this question is that
Adam smith defines
X as Y
in his book. Let analyze basic components of the sentence.
- Subject: Adam Smith
- Object: "economics' -- OR - X.
- Preposition: "in his book" is a preposition phrase of place.
The rule is
NEVER put preposition of time/place between Subject and Object. This is a basic grammar rule in English.
In his book, Wealth of Nations, Adam Smith, generally regarded as the father of economics, defines 'economics' as the 'science of wealth'.
A. In his book,
Wealth of Nations, Adam Smith, generally regarded as the father of economics, defines
Correct. - Regarded as ... --> correct idiom
- Preposition of place is put at the right position.
B. Adam Smith, generally considered to be the father of economics, in
Wealth of Nations, defines
Wrong. - B violates the rule by putting preposition between S and O --> readers may understand that Adam Smith is generally regarded as the father of economics in his book.
- "consider to be" is wrong idiom. The correct one is "consider X Y".
C. In
Wealth of Nations, Adam Smith, generally regarded to be the father of economics, defines
Wrong. - "Regarded to be" is wrong idiom.
- C omits "his" in the phrase "in his book" --> changes meaning, because readers may understand that Adam Smith defines XYZ.... in the book Wealth of Nations, which may not be his own book.
D. Adam Smith, generally regarded the father of economics, in his book,
Wealth of Nations, defines
Wrong. Same error as in B. Putting preposition of place between S and O always creates ambiguity.
E. The father of economics, Adam Smith, defines 'economics', in his book
Wealth of Nations as
Wrong. Same error as in B. Putting preposition of place between S and O always creates ambiguity.
Hope it helps.