In which sentence is the word ‘past’ used as a preposition?

✅ কেন সঠিক: In ‘she’s past her prime’, ‘past’ is followed by an object (‘her prime’) and shows relation, so it is a preposition meaning ‘beyond’.

❌ অন্য অপশন: ‘a thing of the past’ and ‘look back on the past’ use ‘past’ as a noun; ‘ran past’ uses it as an adverb (no object).

💡 মনে রাখুন: past + object = preposition; past alone after verb = adverb; the past = noun.

📖 শব্দার্থ: past her prime — যৌবন বা সেরা সময় পেরিয়ে গেছে।