Step 1: Concept
Volatile oils are complex mixtures where one or two "active constituents" define the drug's character.
Step 2: Meaning
Matching the drug to its primary chemical marker is fundamental to pharmacognosy.
Step 3: Analysis
Sandalwood (A) is defined by Santalols (IV). Rosemary (B) contains Borneol (III). Dill (C) is characterized by Carvone (II). Parsley (D) contains Apiole (I).
Step 4: Conclusion
The correct matching is A-IV, B-III, C-II, D-I.
Final Answer: (A)