function : it's used to describe a an action that was completed before another past action

past perfect focuses in the result of the action

examples : She had finished her h.w before her parents arrived

Key expressions : Before /after/by the time / already/ just

function: it's used to describe an action that was ongoing before another past action

past perfect progresive focuses on the duration of the action

she had been studying for hours before she took a break

important we need to pay attention on the order and duration of the events

key expressions-for-since-before-when-until

Past Perfect Simple

1. By the time she arrived, we had already eaten dinner.

2. He had finished his homework before his parents got home.

3. They had visited Paris twice before moving to France.

Past Perfect Progressive

1. She had been studying for hours before she took a break.

2. We had been waiting for the bus for 30 minutes when it finally arrived.

3. He had been working at the company for five years before he got promoted.