Concept:The expression “It is high time” is followed by a past tense verb to show that an action should happen now.Explanation:“It is high time” means the action is already overdue.In standard English, use the simple past form after this phrase.The subject here is “we”, so the correct past tense form of “stop” is “stopped”.Options like “stop”, “will stop”, and “stops” are not grammatically correct in this structure.Answer:C. stopped