Past perfect (+) s + had + V3 / V ed + c + M s + had + not + V3 / V ed + c + m (?) Had + s + V3 / V ed + c + M?

Since can mean because / as too.
e.g. Since he doesn’t have any friends, he usually spends his time alone. (Because / as he doesn’t have friends)

For
For is used to express a period of time. It can be used as a preposition and conjunction. It means because when it comes as a conjunction.
e.g. I have been living in Paris for 5 years.
For Bob was absent, we didn’t have a lesson.


During / while
During is used before nouns.
While can be used with a sentence or gerund.
e.g. I looked after my brother during vacation.
It was funny to find Jack sleeping during the lesson.
While I was revising the grammar, I found out that I had made many spelling mistakes.