Step 1: Understanding the Question:
This question tests knowledge of pests and diseases of cruciferous crops.
Step 2: Detailed Explanation:
Diamond back moth (A): Plutella xylostella (II).
Club root (B): Plasmodiophora brassicae (I).
Aphids (C): Myzus persicae (IV).
Downy mildew (D): Peronospora parasitica (III).
Thus, the correct matching is A-II, B-I, C-IV, D-III.
Step 3: Final Answer:
Thus, the correct answer is A-II, B-I, C-IV, D-III, which corresponds to option (A).
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