Question

it was because she was seriouslyill that she didn'tcome to the lecture yesterday

because可不可以换做as，for，since??

Answer 1

不能
，虽然在主从复合句
原因状语从句中
我们说表示原因
有as,for,since,because这几个词，但是他们都在语气盒用法上有很大区别的
语气上
because最强，
然后是as
,再是for,最后是since。
用法上，for
一般只能放在句中，表原因。并含有
通过现象推测的含义。
since语气最弱，有‘既然'的意思。
as,表原因
既可以放在
句首也可以放在句中，但语气弱于
because.
既然是强调原因的
强调句
当然用because最强最合适。
强调原因一般那只能用because
和why
两个词
取决于后面接的是原因还是原因导致的结果。
若是原因则用because,若是结果用问why
可替换
she
was
seriously
ill;that
is
why
she
didn't
come
to
the
lecture
yesterday.
后面是个表语从句
在强调句it
is
+强调部分
句型中
我们常用
it
was
because。。句型
所以用
it
was
because
she
was
seriouslyill
that
she
didn'tcome
to
the
lecture
yesterday