Express the same using passive 1. they didn't find the origin of the adjective "big". 2. people easily memorize such idioms. 3. somebody bought a bronze candlestick and three candles. 4. people push the door to open it.

∞1.Тhe origin of the adjective "big" wasn't found.
∞2.Such idioms are easily memorized.
∞3.А bronze candlestick and three candles were bought.
∞4.Тhe door should be pusshed to open.