Concept:After “it is high time”, we use a verb in the past tense.
This structure shows that something should be done now.
Explanation:The phrase “it is high time” is always followed by a past tense verb.
This past tense does not mean past time.
It expresses a present or future need.
For example: “It is high time we left.”
Another example: “It is high time we went.”
In this sentence, the correct verb form after “we” is “started”.
Therefore, the right option is “started”.
Answer:D. started