Concept:The sentence is in the past tense, so the verb in the blank must also be past tense to show the cause of being late.Explanation:The main clause is “Our teacher was late,” which uses the past tense “was.”The reason for being late is “because he __________ a flat tyre.”This also needs a past tense verb: “he had a flat tyre.”The other options (“will have,” “is having,” “has”) are not past tense.Answer:A. had