1. As he had drunk too much, he didn't drive home himself.
=> He didn't drive home himself because he had drunk too much
2. The teacher was impressed by Michael's work, so she gave him the highest score.
=> The teacher was impressed by Michael's work. Therefore ,  she gave him the highest score.
3. Because he hadn't studied hard enough for his exam, Tom couldn't pass it.
=> Tom hadn't studied hard enough for his exam , so he couldn't pass it
4. As I haven't received all the applications yet, I am not eager to hire anyone.
=> I am not eager to hire anyone because I haven't received all the applications yet
5. As I have an assignment to finish, I cannot come with you.
=> I cannot come with you since  I have an assignment to finish