Select the option that expresses the given sentence in direct speech.
He asked me when I had booked the flight tickets.

To convert the indirect speech sentence back into direct speech, we can analyze the grammatical rules of tense changes and pronoun changes in reverse:

1. Identify the reporting verb and tense:
The indirect sentence has "He asked me", which shows that a question was asked. In direct speech, this reporting verb commonly changes back to "He said to me," followed by a comma and quotation marks.

2. Analyze the tense change:
In the indirect speech, the subordinate clause is in the past perfect tense: "...when I had booked the flight tickets."
According to standard rules of reported speech, the past perfect tense in indirect speech is converted back from either the simple past tense or the present perfect tense in direct speech. Let's look at the options:
- "When did you book..." is in the simple past tense.
- "When do you book..." is in the simple present tense.
- "When are you booking..." is in the present continuous tense.
Therefore, the simple past tense "did you book" is the correct tense to revert from "had booked".

3. Analyze the pronoun change:
The first-person pronoun "I" in the indirect clause "I had booked" refers back to the person being spoken to (the listener "me"). In direct speech, this becomes the second-person pronoun "you".

4. Construct the direct speech sentence:
Combining these rules, we get:
He said to me, “When did you book the flight tickets?”

Therefore, the correct option is: He said to me, “When did you book the flight tickets?”