“Where will you be tomorrow,” I said, “in case I have to ring you?”

The correct answer is: B. I asked where he would be the next day in case I had to ring him.

The sentence “Where will you be tomorrow,” I said, “in case I have to ring you?” is a question. The speaker is asking the listener where they will be the next day, in case the speaker needs to ring them. The speaker is using the word “ring” to mean “telephone.”

Option A is incorrect because the speaker is asking the listener where they will be, not where the speaker will be.

Option C is incorrect because the speaker is asking a question, not making a statement.

Option D is incorrect because the speaker is asking about the listener’s whereabouts, not their own.