Concept:
String instruments are arranged here according to increasing number of strings.
Step 1: Identify the instrument with least strings.
Ektaara means a one-stringed instrument.
So:
\[
D = \text{Ektaara}
\]
Step 2: Place Violin.
Violin generally has four strings.
So:
\[
B = \text{Violin}
\]
Step 3: Place Sitaar.
Sitaar has more strings than violin, including main strings, drone strings and sympathetic strings.
So:
\[
A = \text{Sitaar}
\]
Step 4: Place Santoor.
Santoor has a large number of strings.
So, it comes last:
\[
C = \text{Santoor}
\]
Step 5: Final arrangement.
Therefore:
\[
D \rightarrow B \rightarrow A \rightarrow C
\]
Hence:
\[
\boxed{\text{(C) D, B, A, C}}
\]