Option 1 -> Incorrectly matches "At the drop of a hat" with "Reveal a secret" and "Once in a blue moon" with "Immediately, without hesitation."
Option 2 -> Correctly matches all proverbs: "At the drop of a hat" means immediately; "Cost an arm and a leg" means very expensive; "Let the cat out of the bag" means reveal a secret; "Once in a blue moon" means very rarely.
Option 3 -> Incorrectly matches "At the drop of a hat" with "Very rarely" and "Once in a blue moon" with "Very expensive."
Option 4 -> Incorrectly matches "At the drop of a hat" with "Very expensive" and swaps other meanings incorrectly.
Hence, Option 2: (A) - (II), (B) - (III), (C) - (IV), (D) - (I) -> These are common English idioms where "at the drop of a hat" describes instant action, "cost an arm and a leg" emphasizes high price, "let the cat out of the bag" refers to disclosing secrets, and "once in a blue moon" indicates rare occurrences -> correct