They are talking . . . . . . . . a confidential matter, so do not interrupt. A. in B. on C. for D. over

The correct answer is: about.

The word “about” is used to indicate the subject of a conversation. In this case, the people are talking about a confidential matter.

The other options are not correct because they do not indicate the subject of the conversation. The word “in” is used to indicate location, the word “on” is used to indicate position, the word “for” is used to indicate a purpose, and the word “over” is used to indicate a period of time.

Here are some examples of how the other options could be used in a sentence:

• The meeting is in the conference room.
• The book is on the table.
• I am doing this for you.
• The game is over.