Oh, sorry - it's the postman. Excuse me one minute please!
Someone is knocking on my door. I'll be right back!
To be right/straight back - to be right back or to be straight back means that you will go away briefly. You are explaining that your absence will be short.
"I'm going to the supermarket quickly and will be straight back."
Excuse me one minute - this means that you will be absent for a short time. 'One minute' may not literally be a minute - it could be a few minutes and is not a precise indication.
To be right/straight back - しばらくここを離れるけど、すぐに戻ってくると説明しています。
例文
"I'm going to the supermarket quickly and will be straight back."
ちょっとスーパーに行ってくるけど、すぐに戻ってきます。
Excuse me one minute - 少しこの場を離れるということです。
'One minute'は文字通り1分ということではなく、数分になることもあり、
正確な時間を表しているのはありません。
レッスン中に宅急便や郵便が来てレッスンを中断したい時は、
One moment, please. The delivery service is here.
One moment, please. The postman is here.
などがいいと思います。
私（ミチコ先生）もDMMのレッスンを受けているのですが、レッスン中に、宅急便（郵便）やお客さんが来ることがあって、
"Hold on, I heard the doorbell. I'll be right back."という感じで言って、席を離れています。
The mail is here and I need to get it. Please excuse me and I will be right back.
Oops! I hear the mailman and need to go get it. I will be right back. Please wait.
Using "please", "excuse me", or even "one minute please" are all good expressions. Saying "please" lets them know that you are being courteous and value their time. You could even say, "Can you wait just a minute? I need to get the mail real quick." This question gives them the option to say "no" but they usually won't because you included them in the decision and they feel that you value them.
Please excuse me, I must get the mail.
The mail is here and I need to get it. Please excuse me and I will be right back.
Oops! I hear the mailman and need to go get it. I will be right back. Please wait.
"please" "excuse me" "one minute please"、これらはどれも良い表現です。
"please" を使うと、丁寧さ、そして相手の時間を大切に思っていることが伝わります。
次のように言うこともできます。
"Can you wait just a minute? I need to get the mail real quick."（ちょっと待ってもらえますか、郵便を取りに行かないといけません）
この質問は相手に"no"と言う選択肢を与えていますが、普通言いません。なぜなら、意思決定に相手を含めたことで、その人のことを大切に思っていることが伝わるからです。
Please excuse me, I must get the mail.
（申し訳ありません、郵便を取りに行かないといけません）
The mail is here and I need to get it. Please excuse me and I will be right back.
（郵便を取りに行かないといけません。すみません、すぐに戻ります）
Oops! I hear the mailman and need to go get it. I will be right back. Please wait.
（郵便屋さんが来たので行かないといけません。すぐに戻ります、待っていてください）
I'm sorry the postman is at the door, I'll be right back!
There's someone at my door, I'll be straight back
If you are briefly going away but will be back in a little time literally a minute or 2 then you would say 'I'll be right back' or 'I'll be straight back' the person then knows you won't be long
少しの間そこを離れてまたすぐに、それこそ1、2分で戻るなら、
'I'll be right back'（すぐに戻ります）
や、
'I'll be straight back'（すぐに戻ります）
と言えます。
このように言えば、すぐに戻ってくることが伝わります。
Please excuse me for a minute, there is someone at the door.
Please hold on a minute, there is someone at the door.
You can use any of these statements to indicate that someone at the door, and that you will be right back:-
1. Please excuse me for a minute, there is someone at the door.
2. Please hold on a minute, there is someone at the door.
Both of these statements indicate that there is someone at your door that you have to attend to, and that you are asking the teacher to hold on for a minute.
どちらの文でも、玄関に今人が来ていること、そして、すぐに戻ってくるつもりであることを伝えることができます。
1. Please excuse me for a minute, there is someone at the door.（ちょっと失礼します。玄関にお客さんが来ました）
2. Please hold on a minute, there is someone at the door.（ちょっと待ってください。玄関にお客さんが来ました）
どちらの文でも、玄関にお客さんが来たことを伝えて、少し待っていて欲しいとお願いしています。
I think someone's at the door. Excuse me for a moment.
"Give me a second. I'll be back." can be used when something gets your attention and you want to check out what you heard, where you will return afterwards.
"Give me a second. I'll be back."（ちょっと待っていてください。すぐに戻ります）
これは、何かを確認してまた戻ってくるつもりのときに使えます。
"There's someone at my door, i'll be back as soon as possible"
If you are in the middle of an online English lesson and you are interrupted by the postman, who is there to deliver your mail, you could say one of the following : "There's someone at the door. I'll be right back", "The postman is here" or "There's someone at my door, I'll be back as soon as possible". All three of these sentences explain what has happened to your teacher.
英語のオンラインレッスンの最中にもし郵便配達の人が来たら、次のように言えます。
"There's someone at the door. I'll be right back"（玄関に誰か来ました。すぐに戻ります）
"The postman is here"（郵便配達の人が来ました）
"There's someone at my door, I'll be back as soon as possible"（玄関に誰か来ました。できるだけ早く戻ります）
上記どの文でも、この状況について説明できます。
イギリス 
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