I told the tailor to put red buttons . . . . . . . . the dress he is making for me. A. in B. at C. on D. over

The correct answer is C. on.

The other options are incorrect because they do not make sense in the context of the sentence.

• Option A, in, is incorrect because buttons are not typically placed inside of dresses.
• Option B, at, is incorrect because buttons are not typically placed at the end of dresses.
• Option D, over, is incorrect because buttons are not typically placed on top of dresses.

The word “on” is the most logical choice because it indicates that the buttons will be placed on the surface of the dress.