由形容词last，next，this等指示代词修饰的名词词组用作时间状语时，前面的介词at, on, in一般省略。 例如： I saw him in the street sometime last week. 上周我在街上见过他。 Please come to school earlier next time. 下次请早点来学校。 We had a grand social gathering last Sunday. 上星期天，我们举行了一次社交界的盛会。