Step 1: Understanding the Buddhist theory of Dependent Origination.
The Buddhist theory of Dependent Origination explains how suffering arises due to interdependent links in the cycle of birth and death:
- A. Trsna (Craving): The root cause of suffering, as desire or craving fuels attachment.
- D. Sparsha (Contact): When a person comes in contact with the sensory world, it gives rise to feelings.
- C. Vedana (Feeling): The sensations or feelings that arise due to contact with the external world.
- B. Upadana (Clinging): The attachment to feelings, which leads to deeper suffering.
Step 2: Conclusion.
The correct sequence is A, D, C, B.
Final Answer:
\[
\boxed{\text{The correct answer is 1. A, D, C, B.}}
\]