"Can I make more than one appointment at one time?" This is asking only if you can make multiple appointments, or reservations, at the dentist at one time. Typically the person would either answer "no", or "yes, you can make [number] appointments at once."
"How many appointments can I make at once?" This question assumes that you already know you're allowed to make multiple appointments and you're asking for the specific amount you're allowed to make.
"Can I make more than one appointment at one time?"（一度に複数の予約をすることは可能ですか）
ここでは、その歯医者で一度に複数の予約をすることが可能であるかのみを尋ねています。相手はたいてい、
"No"（いいえ、できません）
あるいは
"Yes, you can make [number] appointments at once."（はい、一度に [数字] 回分予約できます）
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"How many appointments can I make at once?"（一度に何回分予約できますか）
これは、既に複数の予約ができることは知っていて、具体的に何回分予約ができるのか確認したいときに使えます。
What is the number of reservations that I can make at one time?
"At one time" means at one point in time. This is a good phrase because it can mean any time including right now or in the future. I hope that this helps! :)
"At one time" は「〈現在・未来を含めたあらゆる時間において〉一回につき」という意味です。
参考になれば幸いです！ :)
What's the limit of reservations I can make at once ?
How many reservations can I make at once ?
"一回で何回分予約できるんですか？" という意味です.
What's the limit of reservations I can make at once ?
"一回で予約できる回数の限は何ですか" という意味です.
Sometimes we may need to make certain reservations, possibly for more than one person or for different dates for yourself. This may be in cases such as doctor appointments, dentist appointments, etc.
In these situations, we may ask the person who makes the reservations questions such as:
1) Could I make more than one reservation?
2) How many reservations can I make at one time?
医者や歯医者に行って、複数の人の予約や、異なる日付の予約を取りたいと思うことがあるかもしれません。
そのような状況では、予約をしてくれる人に次のように質問できます。
1) Could I make more than one reservation?（複数の予約をすることは可能ですか）
2) How many reservations can I make at one time?（一度に何回分予約できますか）
When you are making a reservation for a dentist appointment, if you would like to find out how many reservations you can make at the same time, you can simply ask:
"Can I make more than one reservation?"
歯医者の予約をするときに、一度に何回分まとめて予約できるか確認したいなら、次のように言えます。
"Can I make more than one reservation?"（複数回予約することはできますか）
"Is there a limit to reservations that I can make at once?"
If you would like to find out if it is ok for you to make multiple reservations at once at your dentist, you can simply ask "How many reservations can I make at once?" or "Is there a limit to reservations that I can make at once?". Both these questions address what you would like to find out, if you can book more than one appointment at a time, and both questions will get you a direct answer.
歯医者さんで一度に複数の予約ができるか確認したいなら、次のように言えます。
"How many reservations can I make at once?"（一度に何回分まとめて予約できますか）
"Is there a limit to reservations that I can make at once?"（一度にできる予約の数に制限はありますか）
どちらの質問でも、一度に複数の予約ができるか確認できます。どちらの質問にも相手は直接的に答えてくれると思います。
Is it OK if I make a couple of appointments with you now?
How many appointments am I permitted to make at the same time?
If you are making an appointment with a dentist and wish to enquire how many appointments you can make at the same time, then you may use one of the above exampled phrases.
Practically, the first example is the most normal and appropriate. You do not really want to know the maximum number of appointments you can make at one time do you? You only want to make appointments for your personal situation - which possibly may be for 2 or 3 people? Better to concentrate on your own situation than ask unreal questions with no specifics.
Also, other anchors are speaking in terms of 'reservations'. In the case of a dentist or doctor, in the UK, we make 'appointments' not 'reservations'. A reservation reserves something - like a airplane seat or a a hotel room. You are not actually reserving anything at a dentist - you are 'making an appointment'.
アメリカ合衆国 
モロッコ 
南アフリカ 
イギリス 
