Step 1: Understanding the Prasthana Trayam. 
  
The Prasthana Trayam is the threefold foundation of Vedanta, comprising three texts that are central to the philosophy:  
- A. Upanishads: The Upanishads form the foundation of Vedantic philosophy, containing the essence of knowledge and self-realization.  
- B. Srimad Bhagavadgita: The Bhagavadgita is considered the most important scripture in Vedanta, offering moral guidance and explaining the paths to liberation.  
- D. Brahmasutra: This work synthesizes and elaborates on the teachings of the Upanishads and Bhagavadgita, forming the basis of Vedanta philosophy.  
- C. Puranas: The Puranas are important in Hinduism but do not constitute a part of the Prasthana Trayam.  
Step 2: Conclusion.  
The correct answer is 2. A, B and D only.  
  
 
Final Answer:  
\[  
\boxed{\text{The correct answer is 2. A, B and D only.}}  
\]