sensei ni mou itido setumei wo onegaisimasita.

に marks the person the request is directed to.

So in this sentence:

• 先生に = to the teacher
• 説明をお願いしました = made a request for an explanation

A natural way to think about it is:

• X に お願いする = to ask/request X
• Y を お願いする = to request Y

So here:

• 先生に = the person being asked
• 説明を = the thing being asked for

Because 説明 is the thing being requested.

In 説明をお願いしました, the を marks the content/object of the request: an explanation.

So the structure is:

• 先生に = from/to the teacher
• 説明を = an explanation
• お願いしました = requested

This is a very common pattern:

• 先生に質問をお願いしました
• 友だちに手伝いをお願いしました

In each case, を marks what was requested.

もう一度 means one more time or again.

• もう = more / another
• 一度 = one time / once

Together, they mean once more.

So in this sentence, it means the speaker asked for the explanation again.

A very common casual alternative is もう一回, which also means one more time.

• もう一度 sounds a bit more neutral or slightly more formal
• もう一回 sounds more conversational

Because もう一度 modifies the request as a whole: the speaker requested the explanation again.

Japanese adverbs like もう一度 are often placed before the part they modify. Here, it naturally comes before 説明をお願いしました.

You could think of it as:

• 先生に [もう一度 説明をお願いしました]

It is also possible to hear slightly different word orders in Japanese, but this placement is very natural.

It comes from the noun お願い plus する.

So:

• お願い = request / favor
• する = to do
• お願いする = to make a request / to ask for something
• お願いしました = past polite form: requested / asked

This is a very common pattern in Japanese, where a noun combines with する to become a verb.

So grammatically, お願いしました behaves like a verb phrase.

Both can mean asked/requested, but お願いしました is usually softer and more polite.

• お願いしました = polite, often humble-sounding, softer
• 頼みました = more direct, less formal in tone

Since the sentence involves 先生 and sounds polite, お願いしました fits very well.

A learner-friendly way to think about it:

• お願いする often sounds like I asked/requested politely
• 頼む often sounds like I asked someone to do something

Both are possible in many situations, but お願いしました is especially natural when speaking respectfully.

It can naturally suggest either idea in English, and the difference is small.

The Japanese literally focuses on requesting an explanation again. Depending on context, that could be translated as:

• I asked the teacher to explain it again.
• I asked the teacher for another explanation.
• I asked the teacher to explain it one more time.

Japanese often leaves details slightly less explicit than English, and context tells you what exactly was being explained.

Because Japanese often omits subjects when they are understood from context.

In English, you usually need to say I asked. In Japanese, if it is obvious who did the action, the subject is often left out.

So this sentence does not explicitly say I, but in normal context it is understood.

This is extremely common in Japanese.

Because Japanese does not need a topic marker in every sentence.

A full sentence could be:

• 私は先生にもう一度説明をお願いしました。

But if the topic is already clear, 私は is often dropped.

Without は, the sentence still works perfectly as a complete statement. It sounds natural, especially when the speaker is already understood from context.

Yes, they are different in tone and structure.

• 先生にもう一度説明をお願いしました = I asked the teacher for another explanation / I asked the teacher to explain again
• 先生にもう一度説明してもらいました = I had the teacher explain it again / the teacher explained it again for me

The first sentence focuses on the request. The second focuses on the result/benefit received.

Also, お願いしました sounds polite and respectful. It is a good choice when talking about asking a teacher.

Yes, but the sentence structure would change.

For example:

• 先生にもう一度説明してもらうようお願いしました
• 先生にもう一度説明してくださいとお願いしました

These are different constructions.

In your original sentence, 説明をお願いしました treats explanation as a noun and says I requested an explanation.

That is a very neat and natural Japanese pattern:

• noun + をお願いする

So the original version is concise and polite.

It is past polite.

Breakdown:

• お願いする = dictionary form
• お願いします = non-past polite
• お願いしました = past polite

So the speaker is saying that the request already happened.

This does not necessarily mean the explanation already happened; it only clearly tells you that the act of asking took place in the past.

Japanese word order is more flexible than English, as long as the particles make the roles clear.

For example, these can also be natural depending on context:

• もう一度先生に説明をお願いしました。
• 先生に説明をもう一度お願いしました。

But your original sentence is very natural and easy to understand:

• 先生にもう一度説明をお願いしました。

The particles に and を do the important grammatical work, so the order can move somewhat. Still, not every order sounds equally natural, and the original order is a good standard pattern.

Yes. In もう一度, it is read もういちど.

Even though 一度 can sometimes relate to once/one time, the fixed expression もう一度 is a very common set phrase, and the reading is straightforward:

• もう一度 = もういちど

This is worth memorizing as a whole chunk.

Yes, it is polite.

There are several clues:

• お願いしました is polite
• using お願いする with 先生 sounds respectful
• the overall phrasing is softer than a more direct request style

It is not the absolute highest level of formality, but it is definitely polite and appropriate in many normal situations, especially when talking about a teacher.