at, on, in(A) at表示“在某一时刻，某一时点”。如：I get up at 6:00 every day. 我每天6点起床。注：at daybreak在黎明；at noon在中午；at night在夜间；at Christmas在圣诞节期间；at the age of five在五岁时。(B) on表示“在具体某或某天的上、下午”。如：I heard a shot on (the morning of ) March 18. 三月十八日(早晨) 我听到一声枪响。We don’t have classes on Sunday. 星期天我们不上课。(C) in表示“在某世纪、年、季度、月、周”以及泛指的上、下午、晚上。如：in the 20th century在20世纪；in 1999在1999年；in winter在冬季；in September在九月；in the morning/afternoon/evening 在上午/下午/晚上。
名词性从句及不定式、动名词作主语时，谓语动词一般用单数形式。【例如】To finish the work in advance is what he wants.Smoking cigarettes is dangerous to your healthWhat seems easy in theory is difficult in practice.What caused the accident is a complete mystery.但是，what引导名词从句作主语时，其表语是复数形式时，系动词也可以是复数形式。【例如】What we badly need here are qualified teachers.</p 产品：澳博培训供货总量：不限产品价格：议定包装规格：不限物流说明：货运及物流交货说明：按订单
