Let's first talk about the following two sentences:
1- Sara went to bed as soon as she had finished homework.
2- Sara went to bed as soon as she finished homework.
I think your confusion is valid because we use the past perfect when we talk about something that took place before another thing in the past. So the use of the past perfect comes across in the first sentence but the use of the past simple in the second sentence doesn't. Am I right? In fact, we don't need to use the past perfect unless it is necessary or unavoidable to do so. Even if we talk about one action happening before the other one, it is possible to use the simple past for both actions if we think it is not necessary to highlight or emphasize the happening of the earlier action. It sounds natural to avoid using the past perfect where the simple past works, which is used to refer to something or several things happening in sequence (one after another) in the past.
So both of the sentences are grammatically correct. However, I'll prefer the second phrase to the first one.
As for the last two sentences, it is correct to say that "everyone had gone home when Sara got to the party", but it's not grammatically correct to say that "everyone had gone home when Sara had got to the party". It doesn't make sense. In the past perfect when we talk about two events, we use the simple past in one clause and the past perfect in the second clause.
Let's now talk about the following sentence you are confused about:
"Everyone went home when Sara had got to the party".
There is nothing wrong with this sentence, but the meaning is other way round. It means that first Sara got to the party and then every one went home. Look at the
first sentence again. When Sara got to the party, everyone had gone home. Here it means that first everyone went home and then Sara got to the party. Sometimes, one action happens soon after the other action, here we should use the past simple in both clauses such as when Sara got to the party, everyone left, when they saw the police, they ran away, etc.
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Past perfect tenses usually carry an implication that something has happened before or after.
I had talked to her yesterday. (before or after something else, context or previous conversation would normally fill this in)
If you explicitly state "before" or "after" then simple past will do the job fine. Including the have can still be done for a form of emphasis or to indicate that some time passed before the two events.
I talked to her before she arrived. (It's possible you mean that you talked to her and right after that, she arrive)
I had talked to her before she arrived. (You more likely mean that you talked to her, something else may have happened or a while passed, then she arrived.)
I talked to her before she had arrived. (Something else other than you talking to her occurred before or after she arrived.)
There is one situation where the use of past perfect is different and not optional: if it's not referring to an action at a specific time, which means you wouldn't be using before or after to qualify or any time expression like yesterday, etc.
In the past I talked to her (bad, should be: In the past I had talked to her).
In live speech most people don't ponder this very deeply and sometimes the line is blurred between these guidelines.
Best Answer
Most of them are correct, but I'll rewrite them and add corrections below:
The present perfect shouldn't be used in the above examples. The past perfect is more formal than then simple past. In Group 2, No. 1, you would have to use a gerund; therefore, it should be preceded by a possessive adjective ("your").
I hope this might have helped you out. Take care and good luck.
P.S I have left out the article "the" that should precede "office" because I had assumed the question was talking about a political office. I have since been told that the questioner meant "work office"; therefore, it should have an article before the noun "office".