Isn't it about time you _____ to do morning exercises? [ ] A. have begun B. begin C. ha

Isn't it about time you _____ to do morning exercises? [ ] A. have begun B. begin C. had begun D. began

The phrase "it's about time" requires the past tense verb form to express that something should have happened already or should happen now, a subjunctive mood usage. Among the options, "began" (past tense of "begin") fits this structure.

Answer: D