Tôi nghĩ Lan sẽ rất bất ngờ khi mở món quà.

In Vietnamese, you usually do not need a word like that after I think.

So:

• Tôi nghĩ Lan sẽ rất bất ngờ... = I think (that) Lan will be very surprised...

You can sometimes add words to make the sentence feel more explicit in other contexts, but in everyday Vietnamese, leaving out that is completely normal.

Sẽ is a future marker. It shows that something is expected to happen later.

So:

• Lan sẽ rất bất ngờ = Lan will be very surprised

A few useful points:

• sẽ often corresponds to English will
• Vietnamese does not always have to mark future time, especially if the context already makes it clear
• But in this sentence, sẽ helps clearly show that the surprise will happen in the future

Here, bất ngờ means surprised.

Because it comes after rất, it is functioning like an adjective:

• rất bất ngờ = very surprised

Vietnamese words can sometimes be flexible, so bất ngờ can relate to both the idea of surprise and being surprised, depending on context.

In this sentence:

• Lan sẽ rất bất ngờ = Lan will be very surprised

Vietnamese often does not use a verb like to be before adjectives.

In English, you say:

• Lan will be very surprised

In Vietnamese, you say:

• Lan sẽ rất bất ngờ

This is very normal. Adjectives can directly describe the subject without an extra verb.

So do not try to insert là here.
Lan sẽ là rất bất ngờ would sound unnatural.

The most natural interpretation is that Lan is the one opening the gift.

So the sentence means:

• I think Lan will be very surprised when she opens the gift.

Vietnamese often leaves out the subject of the second clause if it is already clear from context.

So:

• khi mở món quà literally looks like when opening the gift
• but naturally it means when she opens the gift

Because Vietnamese often omits repeated subjects when they are easy to understand.

Compare:

• Tôi nghĩ Lan sẽ rất bất ngờ khi mở món quà.
• Tôi nghĩ Lan sẽ rất bất ngờ khi Lan mở món quà.

The second version is understandable, but repeating Lan sounds less natural unless you want emphasis or clarity.

So omission is normal and efficient.

Khi means when.

In this sentence:

• khi mở món quà = when opening the gift / when she opens the gift

Other words can sometimes work too, depending on style and nuance:

• khi = neutral, common
• lúc = also means when, often a bit more conversational in some contexts

For example:

• Tôi nghĩ Lan sẽ rất bất ngờ lúc mở món quà.

This is also understandable, but khi is very natural in the original sentence.

Both are possible, but món quà is a very common and natural way to say a gift or the gift.

Here is the difference:

• quà = gift / present
• món quà = a gift, a present

Món is a classifier-like word often used in the fixed expression món quà. In this phrase, it sounds very natural and idiomatic.

So:

• mở quà = open gifts / open the present
• mở món quà = open the gift

Both can work, but món quà feels a little fuller and more standard as a noun phrase.

Yes. Mở means open.

So:

• mở món quà = open the gift

This refers to physically opening or unwrapping it.

If you wanted to say receive the gift, you would use a different verb, such as:

• nhận món quà = receive the gift

So mở is specifically about opening, not getting.

Yes, very often.

• Tôi nghĩ... = I think...

It is used to give an opinion, guess, or expectation.

In this sentence, it sounds like the speaker is predicting Lan’s reaction:

• Tôi nghĩ Lan sẽ rất bất ngờ... = I think Lan will be very surprised...

It is natural and common.

The overall word order is actually quite similar here.

Vietnamese:

• Tôi nghĩ = I think
• Lan sẽ rất bất ngờ = Lan will be very surprised
• khi mở món quà = when opening the gift / when she opens the gift

So the structure is basically:

• I think + person + future marker + adjective + when-clause

The main differences are:

• no to be before the adjective
• no repeated subject in the when clause
• no word for that

A very literal breakdown would be:

• Tôi = I
• nghĩ = think
• Lan = Lan
• sẽ = will
• rất = very
• bất ngờ = surprised
• khi = when
• mở = open
• món quà = the gift

So a literal version would be:

• I think Lan will very surprised when open the gift

That sounds incomplete in English, but it helps show how Vietnamese grammar works.

A natural English translation is:

• I think Lan will be very surprised when she opens the gift.

In this sentence, Lan is just the person’s name, so it is perfectly fine.

Vietnamese often uses names directly, especially when talking about someone.

Depending on the relationship, age, and social context, people might also say things like:

• chị Lan
• em Lan
• cô Lan

These add social information such as age or status. But the plain name Lan is completely normal in a basic sentence like this.

A rough pronunciation guide is:

• Tôi nghĩ Lan sẽ rất bất ngờ khi mở món quà
• approximately: toy ngee Lang seh zut but-nguh kuh muh mon kwa

A few notes:

• tôi sounds roughly like toy
• nghĩ has the ng sound like in sing, but at the beginning of the syllable
• sẽ has a rising, creaky tone
• rất ends with a t sound
• ngờ begins with ng
• mở and món have different tones, which matter a lot in Vietnamese

The tones are important, so it is best to listen to a native speaker if possible.