Step 1: Understanding Kant's moral philosophy books.
Kant's most important works related to moral philosophy include:
- A. Groundwork of the Metaphysics of Morals: This work outlines the foundation of Kant's moral theory.
- B. Critique of Practical Reason: This book explores the application of reason in moral actions and the role of duty.
- D. Metaphysics of Morals: This work elaborates on Kant's views about moral law and political philosophy.
- C. Critique of Judgment: This book is more focused on aesthetics and teleology, rather than morality.
Step 2: Conclusion.
The correct answer is 2. A, B and D only.
Final Answer:
\[
\boxed{\text{The correct answer is 2. A, B and D only.}}
\]