Der Lehrer bittet uns, kurz nachzudenken, bevor wir abwechselnd unsere Antworten vorlesen.

It has three parts:

1. Main clause: Der Lehrer bittet uns
2. Infinitive phrase: kurz nachzudenken
3. Subordinate clause with bevor: bevor wir abwechselnd unsere Antworten vorlesen

So the sentence is built like this:

The teacher asks us + to think briefly + before we take turns reading our answers aloud

Because bitten takes a direct object in the accusative case.

• der Lehrer = the subject
• uns = the object being asked

So:

• Der Lehrer bittet uns = The teacher asks us
• not Der Lehrer bittet wir

English does not show this difference clearly with we/us in the same way German does with case endings, so this is a very common learner question.

We are.

In Der Lehrer bittet uns, kurz nachzudenken, the understood subject of nachzudenken is uns.

A useful pattern is:

jemanden bitten, etwas zu tun

= to ask someone to do something

So here:

• Der Lehrer bittet uns = The teacher asks us
• kurz nachzudenken = to think briefly

The meaning is not that the teacher is thinking, but that we are being asked to think.

Because this is a zu-infinitive construction.

The verb is nachdenken.
When a separable verb is used with zu, the zu goes between the prefix and the verb stem:

• nachdenken → nachzudenken
• anfangen → anzufangen
• vorlesen → vorzulesen

So nachzudenken is the correct infinitive form after bitten in this structure.

Yes. nachdenken is a separable verb.

You can see that in different forms:

• Ich denke nach.
• Wir denken kurz nach.
• ..., kurz nachzudenken

In the normal present-tense main clause, the prefix often separates:

• Wir denken nach.

But in the zu-infinitive, it becomes one word again:

• nachzudenken

Here kurz is an adverb, not an adjective.

It describes how long or in what way we think:

• kurz nachdenken = think briefly / think for a moment

Because it is functioning adverbially, it does not take adjective endings.

Compare:

• ein kurzer Moment → adjective before a noun
• Wir denken kurz nach → adverb modifying the verb

Because bevor introduces a subordinate clause, and in German subordinate clauses the conjugated verb goes to the end.

So:

• Wir lesen unsere Antworten vor. → main clause
• ..., bevor wir unsere Antworten vorlesen. → subordinate clause

That final position is one of the most important German word-order patterns to learn.

Because vorlesen is also a separable verb, and in a subordinate clause the two parts stay together at the end.

Compare:

• Wir lesen unsere Antworten vor. → main clause, separated
• ..., bevor wir unsere Antworten vorlesen. → subordinate clause, not separated

So both are the same verb, just appearing in different sentence structures.

abwechselnd means taking turns, alternately, or one after another rather than all at once.

So:

bevor wir abwechselnd unsere Antworten vorlesen

means that the people involved will read their answers aloud in turn.

It is an adverb, and it modifies vorlesen.

Because German adverbs often come before the part of the sentence they relate to most closely, and this position sounds natural here.

So:

• bevor wir abwechselnd unsere Antworten vorlesen

places abwechselnd in the middle field, before the object unsere Antworten and before the verb at the end.

You could sometimes move adverbs around in German for emphasis, but this version is very normal and natural.

It is the direct object of vorlesen, so it is in the accusative case.

The verb vorlesen is something you do to a text, answer, story, etc.:

• eine Geschichte vorlesen
• den Text vorlesen
• unsere Antworten vorlesen

Here Antworten is plural, and in the plural, unsere looks the same in both nominative and accusative:

• nominative plural: unsere Antworten
• accusative plural: unsere Antworten

So the form does not change, but the function is accusative because it is the object of vorlesen.

The commas help separate the different parts of the sentence.

• The comma before bevor is there because bevor starts a subordinate clause.
• The commas around kurz nachzudenken mark off the infinitive phrase.

So the commas show the structure clearly:

• Der Lehrer bittet uns,
• kurz nachzudenken,
• bevor wir abwechselnd unsere Antworten vorlesen.

For learners, this punctuation is helpful because it makes the grammar easier to see.