Select the option that expresses the given sentence in direct speech.

He asked me when I had booked the flight tickets.

He said to me, "When did you book the flight tickets?"  

The correct option is: He said to me, "When did you book the flight tickets?"

This is because direct speech is the exact words that someone spoke. In the direct form, the subject and tense of the verb do not change.

The other options are incorrect because they change the direct form of the sentence in some way:

• He said to me, "When do you book the flight tickets?" - This sentence changes the past tense to the present tense.
• He said to me, "When are you booking the flight tickets?" - This sentence changes the tense of the question from past to present.
• He said to me, "When you had book the flight tickets?" - This sentence changes the word order of the question and removes the auxiliary verb "did."