Step 1:
The earliest Vedic texts are the Samhitas.
Step 2:
Brāhmaņas explain ritualistic interpretations of Samhitas.
Step 3:
Āraņyakas developed next, followed by Upanişads containing philosophical teachings.
Step 4:
Hence, the order is:
\[
B \rightarrow D \rightarrow C \rightarrow A
\]
Thus, the correct answer is:
\[
\boxed{\text{(2)}}
\]