Alice: When will you go to Kenting?
Aaron: We'll go there ____ August.
(A) by (B) with (C) on (D) in
The answer is option D. Is option A also acceptable?
Not as an answer to that simple question without a great deal of other context.
As a test question, D is the correct answer.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.