YOU SAID:

and you had better give me that letter at once, and explain why you never sent it.

INTO JAPANESE

あなたはすぐにその手紙を私に与えたほうがいいですし、それを送ったことがない理由を説明してください。

BACK INTO ENGLISH

You should give the letter to me at once and explain why you have not sent it.

INTO JAPANESE

あなたはすぐに私に手紙を与え、あなたがそれを送っていない理由を説明しなければなりません。

BACK INTO ENGLISH

You must immediately give me a letter and explain the reason why you are not sending it.

INTO JAPANESE

あなたはすぐに私に手紙を与え、それを送っていない理由を説明しなければなりません。

BACK INTO ENGLISH

You must immediately give me a letter and explain the reason why you are not sending it.