从句的连词可以分为几类，主要包括：

普通连词 ：这些连词连接两个句子成分，不引导从句。

after

as

before

since

till

until

when

while

表示“一……就……”的连词 ：这些连词表示两个动作紧接着发生。

as soon as

the moment

the minute

the second

immediately

directly

instantly

once

hardly…when

no sooner…than

含有时间的连词 ：这些连词表达时间关系。

everytime

each time

the next time

anytime

the last time

the first time

by the time

名词性从句的连接词 ：这些连词在名词性从句中充当不同的成分。

连词（不充当成分，无词汇意义）：that, whether, if, as if, as though

连接代词（充当成分，有词汇意义）：what, whatever, who, whoever, whom, whomever, whose, which, whichever

连接副词（充当成分，有词汇意义）：when, where, how, why, whenever, wherever, however

状语从句的连接词 ：这些连词引导状语从句，表达时间、地点、原因等关系。

时间状语从句：when, whenever, while, as, before, after, till, until, not…until, since, ever since, once, as soon as, the moment, the second, immediately, instantly, directly, hardly…when, scarcely…when, no sooner…than

地点状语从句：where, wherever

原因状语从句：because, since, as, for

以上就是一些常见的从句连词及其分类，它们在句子中起着连接作用，并帮助构建复杂的句子结构