Я не расслышал, что сказал учитель, потому что в коридоре было шумно.

Yes. Russian often drops subject pronouns when they are clear from the verb form.

So Я не расслышал... could also be just Не расслышал... in context.

Including Я makes the subject more explicit and can add a little emphasis, like I didn’t catch it.

Because расслышал is masculine singular past tense, it already tells us the speaker is I or he in the right context. Adding Я removes any possible ambiguity.

Не расслышал means didn’t catch / didn’t make out what was said clearly enough.

This is slightly different from не услышал, which more simply means didn’t hear.

• не услышал = I did not hear it at all
• не расслышал = I heard something, but not clearly enough to understand the words

In this sentence, не расслышал is a very natural choice because the problem was noise in the corridor, so the speaker could not make out the teacher’s words clearly.

Russian past tense is commonly formed with -л.

The basic infinitive is расслышать.
Past tense:

• расслышал = masculine singular
• расслышала = feminine singular
• расслышало = neuter singular
• расслышали = plural

Since the speaker here is understood as masculine, the sentence uses расслышал. A female speaker would say:

Я не расслышала, что сказал учитель, потому что в коридоре было шумно.

Both word orders are possible in Russian:

• что сказал учитель
• что учитель сказал

Russian word order is more flexible than English word order.

In this sentence, что сказал учитель sounds very natural and neutral. It keeps the focus on what was said.
Что учитель сказал is also possible, but it may sound slightly more conversational or shift the emphasis a bit toward the teacher as the speaker.

So the version in the sentence is simply a standard, natural order.

Yes, что can mean both what and that, depending on context.

Here, in Я не расслышал, что сказал учитель, it means what:

• I didn’t catch what the teacher said

But in other sentences, что can introduce a content clause like English that:

• Я знаю, что учитель пришёл. = I know that the teacher arrived.

So you identify the meaning from the structure and context.

Because учитель is the subject of the clause что сказал учитель.

In that clause:

• учитель = the one doing the action
• сказал = said

So nominative is correct.

If teacher were an object instead, you would expect a different case. But here the teacher is the person who spoke.

Russian uses commas to separate subordinate clauses more regularly than English does.

Here, что сказал учитель is a subordinate clause connected to the main clause Я не расслышал.

So Russian writes:

Я не расслышал, что сказал учитель...

That comma is required.

Because потому что introduces another subordinate clause:

• main idea: Я не расслышал, что сказал учитель
• reason clause: потому что в коридоре было шумно

Russian normally puts a comma before потому что, just as English often does before because in longer sentences.

So the second comma is also required.

Потому что means because and is the most common neutral way to give a reason.

So:

...потому что в коридоре было шумно
= ...because it was noisy in the corridor

There are other ways to express cause in Russian, but потому что is the standard everyday choice and fits this sentence perfectly.

Because в коридоре answers the question where?, not where to?

• в коридоре = in the corridor / inside the corridor → location
• в коридор = into the corridor → motion toward

Here the sentence describes where the noise was, so the prepositional case is used:

• в коридоре

Because Russian often uses a special impersonal construction to describe conditions:

• было шумно = it was noisy

Here, шумно is not an adjective agreeing with a noun. It is a predicative adverb/state word meaning noisy in the sense of there was noise / it was noisy.

So:

• было шумно = correct for describing the environment
• был шумный = not correct here

If you wanted an adjective, you would need a noun:

• коридор был шумный is awkward and usually not what you want
• more natural: в коридоре было шумно

Good question. In Russian, impersonal sentences about weather, atmosphere, and general conditions often use neuter singular past tense:

• было холодно = it was cold
• было темно = it was dark
• было шумно = it was noisy

There is no real subject noun here. The neuter form было is just the normal form for this kind of impersonal statement.

So было шумно does not mean a neuter thing was noisy; it is simply the standard Russian way to say it was noisy.

Yes, it could:

Я не расслышал, что сказал учитель, так как в коридоре было шумно.

This also means I didn’t catch what the teacher said, since it was noisy in the corridor.

However:

• потому что is more common and neutral in everyday speech
• так как can sound a bit more formal or written

So the original sentence is the most natural everyday version.

The verb расслышал comes from расслышать, which is perfective.

That matters because the speaker is talking about a single completed situation in the past: at that moment, he failed to catch what the teacher said.

If you used an imperfective verb, the meaning would shift toward process, repetition, or background context. But here the point is the result: I didn’t catch it.

So the perfective verb is a very natural choice.

Not very naturally. A rough word-for-word version would be something like:

I not made-out, what said teacher, because in corridor was noisy.

That shows how Russian is built, but it is not good English.

Natural English would be:

• I didn’t catch what the teacher said because it was noisy in the corridor.
• I couldn’t make out what the teacher said because it was noisy in the hallway.

So when learning Russian, it helps to understand the grammar of the Russian sentence rather than trying to match every word directly to English word order.