Do not confuse besides, except, except for, and unless. You use besides to introduce extra things in addition to the ones you are mentioning already. Fruit will give you, besides enjoyment, a source of vitamins. However, note that if you talk about 'the only thing' or 'the only person' besides a particular person or thing, besides means the same as 'apart from'. He was the only person besides Gertrude who talked to Guy. You use except to introduce the only things, situations, people, or ideas that a statement does not apply to. All of his body relaxed except his right hand... Travelling was impossible, except in the cool of the morning. You use except for before something that prevents a statement from being completely true. The classrooms were silent, except for the scratching of pens on paper... I had absolutely no friends except for Tom.Unless is used to introduce the only situation in which something will take place or be true. In the 1940s, unless she wore gloves a woman was not properly dressed... You must not give compliments unless you mean them.

不要混淆 besides, except, except for 和 unless。besides 用于引出已提及事物之外的其他事物：Fruit will give you, besides enjoyment, a source of vitamins（水果不但好吃，而且富含维生素）。但应注意，用于谈论除某人或某物之外唯一的人或物时, besides 的意思与 apart from 相同：He was the only person besides Gertrude who talked to Guy（除了格特鲁德以外，他是唯一和盖伊说话的人）。except 用来引出陈述中唯一不适用的事物、情形、人或想法：All of his body relaxed except his right hand（除了右手以外，他全身上下都放松了），Travelling was impossible, except in the cool of the morning（除了在凉爽的早晨，其他时候出门是不可能的）。except for 用于引出使某说法不能完全成立的事物：The classrooms were silent, except for the scratching of pens on paper（除了钢笔在纸上发出的沙沙声，教室里一片寂静），I had absolutely no friends except for Tom（除了汤姆，我一个朋友也没有）。unless 用于引出某事发生或成立所必需的条件：In the 1940s, unless she wore gloves a woman was not properly dressed（在20世纪40年代，女人若不戴手套就是着装不得体），You must not give compliments unless you mean them（除非出自真心实意，否则不要随便恭维）。