Checking the sentences, putting one verb in each sentence into the past simple, and the other verb into the past perfect.
They (eat) everything by the time I (arrive) at the party.
They ate everything by the time I had arrived at the party.
They had eaten everything by the time I arrive at the party.
They eat everything by the time I arrived at the party.
They had eaten everything by the time I arrived at the party.
When we (leave) the beach, the rain (already start).
When we had left the beach, the rain already started.
When we had left the beach, the rain already start.
When we left the beach, the rain already started.
When we left the beach, the rain had already started.
The car (go) when I (look) into the street.
The car went when I look into the street.
The car went when I had looked into the street.
The car had gone when I had looked into the street.
The car had gone when I had look into the street.
The patient (already die) by the time I (see) her.
The patient had already died by the time I see her.
The patient already died by the time I had seen her.
The patient had already died by the time I saw her.
The patient already died by the time I saw her.
(You already leave) when the trouble (start)?
Did you already leave when the trouble had started?
Did you already leaved when the trouble had started?
Had you already left when the trouble started?
Had you already left when the trouble had started?
By the time I (get) into the town, the shops (close).
By the time I got into the town, the shops closed.
By the time I got into the town, the shops had closed.
By the time I had gotten into the town, the shops had closed.
By the time I had gotten into the town, the shops closed.
The post (not arrive) when I (leave) the house this morning.
The post had not arrived when I had left the house this morning.
The post did not arrive when I left the house this morning.
The post had not arrived when I left the house this morning.
The post did not arrive when I had left the house this morning.
when the police (arrive), the car (go).
when the police arrived, the car went.
when the police arrived, the car had gone.
when the police had arrived, the car had gone.
when the police had arrived, the car went.