481. once and for all =once and forever永远地 all at once (=suddenly, now) 立即,马上

once in a while (=occasionally) 偶尔 (just) for once 就这一次

480. it occurs to sb. that… 某人想到…

479. occupy oneself with (in) 忙于(某事)

478. by occasion of (=because of) 由于

477. on occasion(=now and then)不时地,必要时

476. objection to (接动名词) 反对

475. object to (=be opposed to) 反对

474. take notice of (=pay attention) 注意

473. until further notice 在另行通知前

472. do sth. at short notice 只给很少时间准备