since when引导原因状语从句的区别

Question

it's down to you to pick up the lecture to give us the report tomorrow.
Yes,but how can i pick him out _____I'm in the dark about his appearences?
填when 为什么不填since 不都是既然的意思吗

Answer 1

同时,状语从句是句子的状语由一个从句充当，来修饰主句中的动词，形容词或副词等。状语从句都由从属连词引导，与主句连接，放在句末时，一般不在前面加逗号。
状语从句根据它表示的意思可分为时间，原因，条件，比较，结果，目的等类。下面我们拣重点的一个一个来分析。
时间状语从句：是由when, as, while, after, before, since, until, as soon as 等从属连词引导的状语从