Once in a blue moon

Correct — C, rarely. The idiom 'once in a blue moon' describes something that happens very seldom — an actual blue moon (a second full moon within one calendar month) is itself an uncommon event — so 'rarely' states its meaning.

Why the others are wrong

• (a)
  romantic moment — The phrase is about how often something happens, not about romance; the word 'moon' misleads towards this choice.
• (b)
  occasionally — 'Occasionally' means from time to time, a higher frequency than the 'very seldom' sense the idiom carries.
• (d)
  often — This is the opposite of the idiom, which stresses rarity rather than frequency.

An idiom item — 'once in a blue moon' is a fixed expression meaning something happens very seldom, so the answer is its figurative meaning rather than any literal reading of 'moon'.

No directly related past PYQ was found.

• practice — not a real PYQ

  Choose the option that best states the meaning of the idiom 'few and far between'.

  • (a)happening very often
  • (b)rare and infrequent
  • (c)close together
  • (d)evenly spread out
  Answer(b) rare and infrequent — 'few and far between' describes things that occur seldom.
• practice — not a real PYQ

  Choose the option that best states the meaning of the idiom 'at the drop of a hat'.

  • (a)very reluctantly
  • (b)immediately and without hesitation
  • (c)only after careful thought
  • (d)when reminded repeatedly
  Answer(b) immediately and without hesitation — one acts at once when the occasion arises.