basu no naka de hon wo yomu to, hakike ga surukoto ga arimasu.

A natural breakdown is:

• バスの中で = on the bus / inside the bus
• 本を読むと = when I read a book
• 吐き気がすることがあります = there are times when I feel nauseous / I sometimes feel nauseous

So the overall structure is:

• [Place] で
• [Action] と
• [Result / thing that happens] ことがあります

A very natural English rendering is:

• When I read a book on the bus, I sometimes feel nauseous.

Both can be possible, but バスの中で is more specific.

• バスで can mean by bus or on the bus, depending on context.
• バスの中で literally means inside the bus, so it clearly focuses on the location where the reading happens.

Because the sentence is about getting nauseous while reading inside the bus, バスの中で makes the setting very clear.

Compare:

• バスで本を読む = read a book on the bus / while traveling by bus
• バスの中で本を読む = read a book inside the bus

The second one feels a little more concrete and physical.

The particle で marks the place where an action happens.

Here:

• バスの中 = the inside of the bus
• バスの中で = in the bus / on the bus, as the place where the action occurs

Since 本を読む is an action, the location of that action is marked with で.

A similar example:

• 部屋で勉強します = I study in my room
• 電車の中で寝ます = I sleep on the train

So in your sentence, で tells us where the reading happens.

Here, と means something like when or if and connects the action to a result.

• 本を読むと、吐き気がする = When I read a book, I feel nauseous

In this kind of sentence, A と B often means:

• when A happens, B happens
• if A happens, B happens
• a regular or predictable result

So this is not the quotation particle と. It is the conditional/result と.

In this sentence, it sounds like a habitual reaction:

• When I read on the bus, that tends to make me feel sick.

Before grammar patterns like the conditional と, Japanese uses the plain form.

So:

• 読む + と = correct
• 読みます + と = not correct here

This is very common in Japanese grammar. Many structures attach to plain forms, including:

• 読むと
• 読んだら
• 読むなら
• 読むので

Even in a polite sentence ending with あります, the earlier verb can still be plain:

• 本を読むと、吐き気がすることがあります。

This mix is completely normal.

吐き気 means nausea or the feeling that you might vomit.

吐き気がする literally means:

• nausea occurs
• or more naturally, I feel nauseous

This is a set expression. Japanese often uses Noun + がする for sensations or things perceived.

Examples:

• 音がする = I hear a sound
• いい匂いがする = it smells good
• 寒気がする = I feel chills
• 吐き気がする = I feel nauseous

So you should learn 吐き気がする as a chunk.

Because する in this expression does not take 吐き気 as a direct object.
Instead, 吐き気 is treated as the thing that occurs or is felt, so it takes が.

That is why Japanese says:

• 吐き気がする
• not 吐き気をする

This is just how the expression works idiomatically.

The same pattern appears in:

• めまいがする = I feel dizzy
• 頭痛がする = I have a headache
• 気がする = I feel like / it seems

So the best approach is to memorize 吐き気がする as a fixed expression.

Here, V-plain + ことがあります means:

• there are times when...
• sometimes...
• occasionally...

So:

• 吐き気がすることがあります = I sometimes feel nauseous
• literally, there are occasions when nausea happens

This pattern is often used to describe something that happens from time to time, not always.

Examples:

• 忙しいと、朝ごはんを食べないことがあります。
  = When I’m busy, I sometimes don’t eat breakfast.

• この薬を飲むと、眠くなることがあります。
  = This medicine may sometimes make you sleepy.

In your sentence, it softens the statement a little compared with saying it happens every time.

This is a very important difference.

1. V-plain + ことがあります

This means sometimes do or there are times when ... happens.

• 吐き気がすることがあります
  = I sometimes feel nauseous

2. V-ta + ことがあります

This means have done as life experience.

• 日本へ行ったことがあります
  = I have been to Japan

So:

• することがあります = occasional occurrence
• したことがあります = past experience

In your sentence, it is definitely the first one.

Japanese often leaves the subject unstated when it is obvious from context.

In this sentence, the most natural understanding is:

• I sometimes feel nauseous when I read a book on the bus.

Why I?

Because 吐き気がする describes a physical feeling, and in ordinary conversation that usually refers to the speaker unless context says otherwise.

So even though there is no explicit 私は, Japanese listeners naturally understand the subject from context.

If needed, you could say:

• 私は、バスの中で本を読むと、吐き気がすることがあります。

But in many situations, that would be unnecessary.

By itself, A と B often suggests a regular or natural result:

• 春になると、暖かくなる。 = When spring comes, it gets warm.
• これを押すと、ドアが開きます。 = If you press this, the door opens.

In your sentence, though, the ending ことがあります changes the nuance. It tells us that the result does not happen every single time.

So the full sentence means something like:

• When I read a book on the bus, I sometimes feel nauseous.

Not:

• Every time I read a book on the bus, I feel nauseous.

So the sentence expresses a general tendency or occasional result.

Because Japanese politeness is usually determined by the main sentence ending.

Here, the sentence ends with:

• あります — polite

Earlier parts of the sentence can still use plain forms because they are inside grammar structures:

• 読む before と
• する before ことがあります

So this is a normal polite sentence with internal plain forms.

A rough pattern is:

• inside the sentence: plain forms are common
• final verb: often shows the politeness level

That is why this sentence sounds polite overall.

Yes, but the meaning changes.

• 吐き気がします = I feel nauseous
  This sounds more direct, and depending on context it can imply it happens whenever that situation occurs, or that it is happening now as a general fact.

• 吐き気がすることがあります = I sometimes feel nauseous
  This specifically means it happens on some occasions.

So:

• 吐き気がします = stronger / more direct
• 吐き気がすることがあります = softer / occasional

In your original sentence, the speaker is not saying it always happens, only that it happens sometimes.

The comma helps separate the condition from the main result:

• バスの中で本を読むと、
  when I read a book on the bus,
• 吐き気がすることがあります。
  I sometimes feel nauseous.

Japanese commas are somewhat flexible, but here the comma makes the sentence easier to read and understand.

Without the comma, the sentence would still be grammatical:

• バスの中で本を読むと吐き気がすることがあります。

But the comma is natural and helpful.

No. In normal Japanese writing, this sentence would usually be written without spaces:

バスの中で本を読むと、吐き気がすることがあります。

Spaces are often added in learning materials to make word boundaries easier to see.

So the spaced version is learner-friendly, but the standard written form is:

• バスの中で本を読むと、吐き気がすることがあります。

The reading is:

バスの なかで ほんを よむと、はきけが することが あります。

Word by word:

• バス = basu
• 中 = なか
• 本 = ほん
• 読む = よむ
• 吐き気 = はきけ
• することがあります = することがあります

A smooth full reading is:

バスのなかでほんをよむと、はきけがすることがあります。

吐き気がする is very natural and standard. It is a good way to describe nausea.

Some other possible expressions are:

• 気分が悪くなる = to start feeling sick
• 乗り物酔いする = to get motion sickness
• 酔う = to get sick/dizzy from motion, alcohol, etc. depending on context

But each one is slightly different:

• 吐き気がする focuses specifically on nausea
• 気分が悪くなる is broader: feeling unwell
• 乗り物酔いする focuses on motion sickness as the cause

So your sentence is natural if the speaker specifically means nausea.