Do not confuse except, except for, unless, and besides. 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. 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.

不要混淆except，except for，unless和besides。 用except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（除了右手外，他全身都放松了), Travelling was impossible, except in the cool of the morning（除了在凉爽的早晨，其他时候出游都是不可能的）。except for 用于引出使某陈述不能完全成立的事物：The classrooms were silent, except for the scratching of pens on paper（除了钢笔在纸上写字的沙沙声，教室里一片安静），I had absolutely no friends except for Tom（除了汤姆，我真的一个朋友也没有）。unless用来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，否则不要随便恭维别人）。besides用来引出除已经提到的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）。但要注意的是，如果用于谈论除某人或某事物之外仅有的人或物时，besides的意思与apart from相同：He was the only person besides Gertrude who talked to Guy（他是除了格特鲁德外唯一同盖伊说话的人）。