Would you mind . . . . . . . . to the Principal how the trouble started?

The correct answer is: D. explaining

The other options are:

• A. talking: This is not the correct answer because talking is not the same as explaining. Talking can be about anything, but explaining is about providing information or reasons for something.
• B. remarking: This is not the correct answer because remarking is not the same as explaining. Remarking is making a brief comment, but explaining is providing information or reasons for something.
• C. telling: This is not the correct answer because telling is not the same as explaining. Telling is simply communicating something, but explaining is providing information or reasons for something.

In the context of the question, the Principal is asking the speaker to provide information about how the trouble started. This means that the speaker needs to explain what happened and why it happened. The other options do not convey this meaning.