He spoke . . . . . . . . the subject for two hours regularly. A. in B. on C. of D. with

in
on
of
with

The correct answer is C. of.

The preposition “of” is used to indicate the subject of a conversation or discussion. In this case, the speaker is talking about a specific subject for two hours regularly. Therefore, the preposition “of” is the most appropriate choice.

The other options are not as accurate. The preposition “in” is used to indicate a location or position. The preposition “on” is used to indicate a surface or area. The preposition “with” is used to indicate a person or thing that is associated with or involved in something.

Here are some examples of how the preposition “of” is used to indicate the subject of a conversation or discussion:

  • We talked of the weather.
  • I’m thinking of buying a new car.
  • What do you think of the new movie?

I hope this helps! Let me know if you have any other questions.