I had been to Australia before I was 18.
- I played my favorite video game. Because I finished my homework.
I had finished my homework before I payed my favorite video game.
- I ate a piece of cheese cake. I ate a piece of chocolate cake.
二つの事柄が密接に関わっていない（順序や因果関係が不明 な ）のでこういう場合は過去完了で表現しない
- The lady was a teacher before she gad a baby.
The lady had been a teacher before she had a baby.
- Before I arrived at the school, the class already started.
Before I arrived atthe school, the class had already started.
- I lost my wallet which I bought the day before.
I lost my wallet which I had bought the day before.
- My father had been the head of the company before he changed his career.
My father had been the head of the company before he changed his career.
- I washed my face and brushed my teeth.
- He didn’t speak to me until I became calm.
He didn’t speak to me until I had become calm.
He said he had been in his room all the time.
Before their father came home, the family had finished eating.
The boat had been drifting for a week when it was found.