La profesora empezó a murmurar la respuesta mientras miraba el texto.

In Spanish, the definite article is often used where English would just say the teacher or sometimes even simply teacher in context. La profesora means the female teacher.

Also, profesora is specifically feminine. If the teacher were male, it would be el profesor.

Both can mean teacher, but they are not always used in exactly the same way.

• Profesora is very common for teachers in general, especially in secondary school, university, or formal contexts.
• Maestra often refers more specifically to a primary-school teacher, though usage can vary.

So la profesora sounds natural here and may suggest a more general or formal teacher.

Because empezar a + infinitive means to begin/start doing something.

So:

• empezó a murmurar = she started to murmur / she began murmuring
• murmuró = she murmured

The version with empezó a focuses on the beginning of the action, not just the action itself.

Because empezar normally uses the structure empezar a + infinitive.

Examples:

• Empezó a hablar = She started to speak
• Empezaron a correr = They started to run

This a is required by the verb pattern. It does not mean to in a literal movement sense here; it is just part of the construction.

Empezó is the preterite of empezar, and it is used because the sentence presents the start of the action as a completed event in the past.

The preterite is common for:

• single completed events
• changes
• events seen as bounded or finished

Here, she began murmuring is a specific event that happened at a certain moment.

Because miraba describes an ongoing background action: while she was looking at the text.

The imperfect is often used for:

• ongoing actions in the past
• background description
• actions in progress when another event happened

So the contrast is:

• empezó = the main event that began
• miraba = the background action already in progress

This is a very common Spanish pattern:

• Preterite for the event
• Imperfect for the ongoing setting or background

Mientras means while, and it often introduces an action that was happening at the same time as another past action.

In this sentence:

• empezó a murmurar = the action that starts
• mientras miraba el texto = what she was doing at the same time

Using the imperfect after mientras is very natural when the action is ongoing in the background.

It would be much less natural here.

Miró is preterite, so it would suggest she looked at the text as a completed action, rather than she was looking at the text as an ongoing background action.

Since the sentence is describing something happening while she was engaged in looking at the text, miraba is the better choice.

Spanish often uses articles where English does too, and sometimes where English might omit them.

Here la respuesta means the answer, referring to a specific answer. Without the article, respuesta would sound incomplete in this sentence.

So:

• murmurar la respuesta = to murmur the answer

Not usually in this context.

Here el texto most naturally means:

• the text
• the passage
• the written text/document

It could refer to something written that she is reading or consulting.

If you wanted to say text message, Spanish often uses:

• mensaje
• mensaje de texto

So in this sentence, el texto is much more likely a written passage or document, not a phone message.

They are similar, but not identical.

• murmurar = to murmur, to mutter, to speak in a low voice
• susurrar = to whisper

Susurrar is more specifically whispering. Murmurar can suggest a low, not fully clear voice, sometimes almost to oneself.

So empezó a murmurar la respuesta suggests she began saying the answer quietly, perhaps under her breath.

Because Spanish often omits subject pronouns when the verb ending already shows who the subject is.

Here:

• empezó = he/she/it started
• miraba = he/she was looking

The subject is understood from the context, and la profesora is already there, so there is no need to say ella.

Adding ella would usually only be for emphasis or contrast.

Because Spanish normally puts the infinitive verb before its direct object:

• murmurar la respuesta = to murmur the answer

That is the standard order:

• verb + object

You can sometimes change word order for style or emphasis, but in a normal sentence this order is the natural one.

Yes. Comenzó a murmurar is also correct and means basically the same thing: she began to murmur.

In many contexts, empezar and comenzar are interchangeable.
Very roughly:

• empezar is often a bit more common in everyday speech
• comenzar can sound slightly more formal in some contexts

But both are perfectly natural.

Because after empezó a, Spanish uses the infinitive to express the action that began.

So the structure is:

• empezó = started
• a murmurar = to murmur

This works like English started to murmur, though Spanish uses the infinitive much more systematically in these kinds of verb combinations.

They are very close in meaning, but not always identical in feel.

• mientras miraba el texto = simple, natural, and very common
• mientras estaba mirando el texto = also correct, but slightly more explicit about the action being in progress

Spanish often prefers the simple imperfect (miraba) where English might strongly favor was looking. So miraba is the more natural default here.