Step 1: Understanding the South Asian linguistic area.
South Asia is a well-known linguistic area where unrelated languages share common structural features due to long-term contact.
Step 2: Evaluating the features.
Compound verbs are widespread across Indo-Aryan, Dravidian, and other South Asian languages.
Retroflex consonants are a defining phonological feature of the region.
Non-nominative subjects, such as dative or ergative subjects, are commonly found across many South Asian languages.
Step 3: Eliminating the incorrect option.
Agglutinative morphology is characteristic of some languages, especially Dravidian, but it is not shared by the vast majority of South Asian languages.
Step 4: Conclusion.
Therefore, options (A), (B), and (C) correctly describe areal or typological features of South Asian languages.
Final Answer: (A), (B), and (C)