13. Mark said that he ______ a great time in London the previous summer. A had had B would have C has had

The correct answer is A had had. Explanation: 'Had had' is used to express the past perfect tense. The first 'had' is the auxiliary verb for the past perfect, and the second 'had' is the past participle of 'have', indicating that Mark had a great time in London the previous summer. Since it's reported speech about the past, we use the past perfect.