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必修5 Unit 5（2） Remove clothing using scissors if necessary unless it is stuck to the burn.除非衣服紧贴在烧伤面上，否则都要把衣服脱掉。如果需要的话，可以使用剪刀。 unless是连词，意为“除非，如果不”，引导的是一个肯定条件状语从句，从句有时可以与if...not...引导的否定状语从句互换。 ①It is known to all that unless_you_exercise_regularly，you won’t keep fit.众所周知，除非你有规律地锻炼，否则身体不会健康。 ②We will have a picnic in the park this Sunday unless it rains or it’s very cold. 除非下雨或天很冷，我们将在本周日去公园野餐。 ③Unless_you’ve_tried_it，you can’t imagine how pleasant it is. 除非你尝试一下，否则你无法想像那是多么令人愉快。 John was studying in his room when he heard screaming.约翰正在房间里学习，突然听到一声尖叫。 when在此作并列连词用，意为“正在这时；那时”。 be doing...when...正在……这时…… be about to do...when...正打算做……这时…… be just going to do...when...正要……这时…… be on the point of doing...when...正要……这时…… had just done...when刚……就在这时…… | 
