車のトランクはtrunkです。
トランクが開いている、は「Your trunk is open.」
こういう時、英語では代名詞のyourを付けます。
あなたの車のトランク、ということですね。
日本語の感覚では一々「あなたの」と付けると不自然ですが、英語は代名詞が重要です。
また、開いているかどうか確実ではない場合、もしくは少し婉曲な言い方をしたい場合は、I thinkを付けるとクッションになります。
I think your trunk is open.（トランク開いてるんじゃないですか）
ちなみに、trunkは車のトランク（後部の荷物を入れるところ）という意味もありますが、他にも木の幹、大きな旅行鞄、また象の鼻もtrunkです。
ついでに覚えておきましょう。
車のトランクは英語でも trunkです。
シンプルに Your trunk is open.と伝えましょう。
良かったら他にも車に関する文を書いてみました。
参考にどうぞ。
Your headlight is on.
ヘッドライトが付いたままですよ。
Your door is not properly closed.
ドアがちゃんとしまっていませんよ。（半ドアですよ）
Your dome light is on.
ルームランプが付いたままですよ。
If you want to get someone's attention politely then you would start with 'excuse me'
In the Uk we use the word 'boot' meaning the back area of the car (trunk in the US) so you would say
'Excuse me!, your boot is open' this would let the person knows whats happening
相手の気を引くときは、”Excuse me”（すみません、失礼します）と初めに言います。
イギリスでは、”Boot"というのが車のトランクのことです（アメリカではトランクと言います）。
”Excuse me! Your boot is open."（すみません！あなたの車のトランクが開いていますよ）と伝えます。
Native speakers will say like this: “Your trunk is open!”.
There are lots of other ways to say it, but this one is the most accurate and most commonly used.
Here is an example on how to use this in a conversation:
A: Excuse me, sir! Your trunk is open!
B: Oh, I didn't notice. Thanks a bunch!
ネイティブスピーカーは次のように言います。
“Your trunk is open!”
(トランクが空いてます！)
他にもいろいろな言い方ができますが、これが最も正確で一般的です。
以下、会話例です。
A: Excuse me, sir! Your trunk is open! (すみません、トランクが空いてます！)
B: Oh, I didn't notice. Thanks a bunch! (あ、気づきませんでした。どうもありがとう。)
Excuse me but do you know that your trunk is open?
Notice that in both responses I added the "Excuse me" part to make it as polite as possible. When talking to a stranger in most instances, whether it be a statement or question, it's always preferred if you express it in a polite manner. By asking them if they know their trunk is open is to state that it is indeed opened and implying that it's probably best if he/she closes it before it causes any unnecessary problems for them. It can also be viewed as an informative statement to let the driver of the vehicle decide whether or not it should be opened or closed.
どちらの例文にも "Excuse me"（すみません）を加えて、丁寧に伝えています。知らない人に声をかけるときは、それが質問であれ発言であれ、丁寧に表した方がいいです。
"Do you know that your trunk is open?"（トランクが開いているの知っていますか）
これは、何かが起こる前にトランクを閉めた方がいいというニュアンスです。また、運転手がトランクを開けておくべきか閉めるべきかの判断ができるよう情報提供していると見ることもできます。
Excuse me, but I wanted to let you know that your trunk was left open.
If you are approaching someone you don't know, you should say, "Excuse me," to get his/her attention.
You can then state that their car trunk remains open (is still open), or you can ask if they already knew about it. You can do this by saying, "Excuse me, did you know your trunk is open?" This question makes the person aware of the situation.
Instead of asking a question, you can simply say, "I wanted to let you know that your trunk was left open." This lets the person know that you were concerned, and they should tell you if it was on purpose or by accident.
知らない人に近づくなら、"Excuse me"（すみません）と言って相手の注意を引いた方がいいです。
その後、トランクが開いていると伝えるか、トランクが開いていることを知っているか尋ねることができます。例えば：
"Excuse me, did you know your trunk is open?"（すみません、トランクが開いているのご存じですか）
この質問で相手に状況が伝わります。
質問の代わりに、次のように尋ねてもいいです。
"I wanted to let you know that your trunk was left open."（車のトランクが開いています）
このように言うと、トランクが開いていることを心配していたことが伝わります。相手はそれがわざとなのかどうか教えてくれるはずです。
Your boot is open.
Sorry to bother you, but your boot is open.
Excuse me, your boot is open.
When you want to let a driver know that their boot is open, you can use one of these three sentences. They are all more or less the same, however, the second two are much more polite, as you can probably see.
I hope that helps.
Have a good day.
Will
"Your boot is open!" This example lets the person know, very quickly, that they left the boot of their car open.
"Excuse me, you left your trunk open!" By adding "excuse me" to the beginning of this example sentence we are being slightly more polite and alerting the person to the fact that their trunk is open.
Depending on the urgency of the situation, you may have time to say excuse me however if you are short on time, that is, the car is driving right by you, you can just get straight to the point.
A synonym of boot is: trunk. Car boot's or trunks are generally at the rear end of a car and they are used for storage. If a car boot is open when the car is moving it can be dangerous as items could potentially fall out of the boot onto the road, affecting the traffic that is travelling behind that vehicle.
In England we call this a boot. If the boot is open, you could politely tell someone by catching their attention by saying excuse me, and then proceed to tell them their boot is open.
Be aware that your car trunk is not properly closed.
Your boot is open.
Your car trunk is open.
In South Africa we use the word 'boot' to speak of the trunk of a car.
If the car trunk is open it might cause a disturbance when driving over humps or someone might steal what is inside, it is always good to alert drivers if their trunk is not securely shut.
"Your car trunk is not closed."
"Your trunk is open."
"Your car trunk is not securely shut."
"Your car trunk needs to be shut closed."
These are two different ways that you could say this to let someone know that they forgot to close their car trunk and now it's open. You can either use, "your truck," as the subject head of the sentence, or use, "you," with the verb, "to leave," as the main subject of the sentence.
1. The boot of your car is open!
2. Your trunk is open!
The boot or trunk is the main storage space in a vehicle.
The words "boot"and "trunk" are interchangeable. - you can use
one or the other.
You can simply tell the driver of the car in question that their
boot (or trunk which is more commonly used by Americans) is open.
日本 
アメリカ合衆国 
イギリス 
カナダ 
オーストラリア 
ニュージーランド 
南アフリカ 
