Concept:
A stupa is a Buddhist religious monument. It generally contains relics and is used for worship and circumambulation.
Important parts of stupa architecture include anda, harmika, chhatra, vedika, railing elements, sopana, and other structural members.
Step 1: Understand Anda.
Anda is the dome-shaped hemispherical body of the stupa.
It is one of the most important parts of a stupa.
So, D is correct.
Step 2: Understand Sopana and Suchi.
Sopana means steps or stairway.
Suchi is associated with railing elements of the stupa.
So, B and C are correct.
Step 3: Understand Yupa.
Yupa is a pillar-like element and is accepted in the context of early sacred structural traditions.
So, A is correct.
Step 4: Check Sikhara.
Sikhara is the tower or superstructure of a Hindu temple.
It is not a standard element of stupa architecture.
So, E is incorrect.
Therefore, the correct elements are:
\[
A,\ B,\ C,\ D
\]
Hence, the correct answer is:
\[
\boxed{\text{(D) A, B, C and D only}}
\]