The reason ______ Old French made contributions to Middle English is ______ English borrowed many words from it.
He waited until it was dark ____ nobody could see him clearly.
Now there are many _____ in our company.
We should think of ways to stop the waste from the factory _____ our living environment.
As far as I know, this man ____ risk anything than lose the ring for his wife.
She locked her room _____ a thief would break into it.