Concept:Check tense and verb form consistency in the sentence.Explanation:Part (a) “The pollution level is very” is correct.Part (b) “high in our city, and” is correct.Part (c) “becomes a health hazard” has an error.The present simple “becomes” does not fit the current situation.It should be “is becoming” or “has become” a health hazard.So the error is in part (c).Answer:Part (c) contains the error. The correct option is C.