while表对比，when示突然间。 but/yet意转折，(either...) or供挑选， (neither...) nor全否定，not only...
but also...入递进关。
[操作技法1] 弄清楚前后分句之间的逻辑关系，正确理解语境，就可正确解题。 [典例] (2019·福州市高中毕业班适应性练习)Now the library has as many as 3,500 characters, ________ Chen's research on the project still continues, as he plans to extend the library to 7,000 characters.
[解析] 考查连词。 根据语境可知，空处前后内容之间为转折关系。故填but/yet。 [答案] but/yet
[操作技法2] 注意when和while用作并列连词时常用的固定句式和特殊意义。 [典例] (2019·昆明市高三复习诊断测试)During World War Ⅱ， ____________ long underwear was given to US soldiers to keep them warm in the winter cold, it really came to the public's attention.
[解析] 考查连词。分析句子结构可知，空处引导时间状语从句，故用连词when“当……时”；根据语境可知，前后句之间也可以为逻辑上的因果关系，前因后果，故用连词since/as/because。故填when/since/as/because。
[答案] when/since/as/because
二、从属连词在语法填空中的审题、解题要领口诀
状语从句不一般，服务功能它最全。 表原因、表结果，又表让步与时间。 表方式、表比较，尚表目的和条件。 连词作用分辨清，灵活运用不留憾。
[操作技法1] 具备全面的状语从句知识，熟悉每个连接词的语义和语法特征，尤其像as，since，while等引导不同的状语从句的连词，before引导状语从句时可以表达不同的意思等，都要熟练掌握。
[典例] (2019·郑州市高中毕业年级第二次质量预测)____________ he was looking into the use of cellphones by drivers, he found that more than 30% of them reached for their cellphones on the road.
[解析] 考查状语从句。该句意为：当他调查司机使用手机的情况时，他发现30%以上的司机在路上会伸手拿手机。根据句意并结合空后的“he was looking into”可知，空处表示“当……时”，故填When/While/As。
[答案] When/While/As
[操作技法2] 正确理解语境，这是正确答题的关键。需要提醒的是，在时间状语从句中有几个常用的固定句型，一定要牢记。如：be doing sth....when；be about to do sth. when...；
had just done sth. when...; not...until...。
[典例] (2019·高考考试大纲调研卷三)I didn't press the close button ____________ she steadied herself in the lift.
[解析] 考查状语从句。分析句子结构可知，本句是not... until...句型，表示“直到……才……”。
[答案] until
[操作技法3] 巧看句式结构：在复合句的考题中，要首先看一下有没有and，or，but，so等并列连词，这些词可以作为做题的依据。
[典例] (2019·石家庄高中毕业班教学质量检测)He was so att