Step 1: Identifying Kant's Key Moral Philosophy Texts.
Kant's seminal contributions to moral philosophy are found in the following works: - A. *Groundwork of the Metaphysics of Morals*: Establishes the fundamental principles of Kant's ethical system. - B. *Critique of Practical Reason*: Investigates the practical application of reason in moral decision-making and the concept of duty. - D. *Metaphysics of Morals*: Expands upon Kant's theories regarding moral law and its connection to political philosophy. - C. *Critique of Judgment*: Primarily addresses aesthetics and teleology, with less direct focus on morality.
Step 2: Determining the Correct Texts. Based on the scope of these works, the relevant texts for Kant's moral philosophy are A, B, and D.
Final Answer: \[ \boxed{\text{The correct answer is 2. A, B and D only.}} \]