中考和高考英语中常见的连词包括以下几类：

并列连词

表示并列关系：and, both...and..., neither...nor..., not only...but also..., as well as, or, either...or, neither...nor

表示选择关系：either...or..., neither...nor

表示递进关系：besides, furthermore, moreover, in addition, and also

从属连词

引导宾语从句：that, if, whether, who, whom, whose, what, which, whose, why, when, where, how

引导时间状语从句：when, while, before, after, as soon as, since, because, although, if, unless, whether, however

引导让步状语从句：although, but, however, yet, still, so that

引导条件状语从句：if, unless

表示因果关系的连词

表示原因：because, since, as, due to, thanks to

表示结果：therefore, so, as a result, as the result of, because of, due to, owing to

表示对比关系的连词

表示转折：but, however, yet, although

这些连词在中考和高考英语中频繁出现，掌握它们的用法和含义对于提高英语成绩非常重要。建议学生在平时学习和练习中多加注意这些连词的用法，并通过练习题和模拟考试来巩固记忆。