basu no naka de hon wo yomu to, tokidoki hakike ga simasu.

Both are possible, but they emphasize slightly different things.

• 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.

In this sentence, バスの中で本を読む means to read a book while inside the bus / on the bus. Using の中 makes the setting more explicit.

中 means inside or the inside.

So:

• バス = bus
• の = linking particle, like of
• 中 = inside

Together, バスの中 literally means the inside of the bus.

This is a very common pattern:

• かばんの中 = inside the bag
• 家の中 = inside the house
• 箱の中 = inside the box

The particle で marks the place where an action happens.

Here, the action is 本を読む (to read a book), and that action happens in the bus.

So:

• バスの中で = in/on the bus as the location of the action
• 本を読む = read a book

A good way to think about it:

• で = where an action takes place
• に = where something exists, goes, or ends up

Since reading is an action, で is the natural choice.

Because と here is being used as a conditional meaning something like:

• when
• whenever
• if

With this grammar, the verb before と is usually in plain form.

So:

• 本を読むと = when/whenever I read a book

In this sentence, it expresses a regular result: When I read a book on the bus, I sometimes feel nauseous.

This と is often used for things that happen naturally, repeatedly, or automatically.

No. This is not the と meaning and.

Japanese と has multiple uses. Here it is the conditional と, meaning when/whenever/if.

Compare:

• パンと牛乳 = bread and milk
  
  • this is the and use
• これを押すと、ドアが開きます = If/when you press this, the door opens
  
  • this is the conditional use

In your sentence, 読むと is definitely the conditional pattern.

ときどき means sometimes, and it modifies the whole result clause:

• 本を読むと、 = when I read a book
• ときどき吐き気がします = I sometimes feel nauseous

So the meaning is: When I read a book on the bus, I sometimes feel nauseous.

Its placement is natural because it describes how often the result happens, not how often the person reads.

If you moved it earlier, the nuance could shift a little. For example:

• ときどきバスの中で本を読むと… might sound more like when I sometimes read on the bus..., which is less natural here.

吐き気 means nausea or the feeling that you might throw up.

It comes from:

• 吐く = to vomit
• 気 = feeling, sense, mood

But as a vocabulary item, 吐き気 simply means nausea.

It does not mean actually vomiting. It means the unpleasant feeling.

Because する in this expression works with が, not を.

吐き気がする is a set expression meaning:

• to feel nauseous
• literally something like nausea occurs/is felt

So:

• 吐き気がします = polite form of 吐き気がする

This is similar to other expressions with sensations:

• 頭痛がする = to have a headache
• めまいがする = to feel dizzy
• いやな感じがする = to have a bad feeling

So this is something you should learn as a chunk: X がする for certain sensations or feelings.

Because Japanese often uses する for bodily sensations, impressions, and certain feelings.

So instead of saying something like nausea exists, Japanese naturally says:

• 吐き気がする = to feel nauseous

Using です would not work here in the same way.

For example:

• 吐き気です is not the normal way to say I feel nauseous
• 吐き気があります can exist in some contexts, but it sounds more clinical or objective, like there is nausea or I have nausea
• 吐き気がします is the most natural everyday phrasing here

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

In English, you usually need I:

• I sometimes feel nauseous

In Japanese, if the speaker is talking about their own experience, 私 is often omitted:

• ときどき吐き気がします

It is understood as:

• I sometimes feel nauseous

This is extremely common in Japanese.

It sounds like a habitual or repeated situation.

The key clue is 読むと, which often expresses what happens whenever something occurs, and also ときどき, which means sometimes.

So the sentence means something like:

• When I read on the bus, I sometimes get nauseous
• Reading on the bus sometimes makes me feel sick

It is not describing one single event in the past.

Yes, in some contexts と can be translated as if, but here when or whenever is usually more natural in English.

That is because と often describes a predictable or regular result.

So:

• 本を読むと、ときどき吐き気がします = When/whenever I read a book, I sometimes feel nauseous

Using if is not totally wrong, but it can sound a little less natural in English for this kind of repeated, real-world result.

Because を marks the direct object of the verb.

Here:

• 本 = book
• 読む = read

So 本を読む means to read a book.

This is one of the most basic verb patterns in Japanese:

• 音楽を聞く = listen to music
• 映画を見る = watch a movie
• 水を飲む = drink water

Here are the readings:

• バス = basu
• 中 = なか
• 本 = ほん
• 読む = よむ
• ときどき = tokidoki
• 吐き気 = はきけ
• します = shimasu

So the full sentence is read:

バス の なか で ほん を よむ と、ときどき はきけ が します。

Yes. します is the polite form of する.

So:

• 吐き気がする = plain form
• 吐き気がします = polite form

The whole sentence is in polite style because it ends with します.

A plain-style version would be:

バスの中で本を読むと、ときどき吐き気がする。

Yes, the sentence suggests that the nausea happens in the situation reading a book on the bus. It does not strictly separate whether the cause is:

• reading while moving,
• the bus ride itself,
• or a combination of both.

In natural interpretation, most people would understand it as motion sickness caused or worsened by reading on the bus.

So the idea is: When I read on the bus, I sometimes get nauseous.

That is a very natural and common interpretation.