It is the cleanest city in India and second greenest city after Chandigarh. Any other city claiming to be greenest or cleanest has very less population. According to a survey by ABP News-Ipsos, Nagpur has been identified as the best city in India by topping the livability, greenery, public transport, and health care indices.
A relative pronoun makes a connection between an antecedent  an a subordinate clause that gives information about the  antecedent.   The relative pronouns are: who, whomâ¦, whose, which, that.    Examples:   The teacher who assigned the work should answer your  questions.
Now the antecedent (student) is the direct object of the main sentence and should therefore be accusative, but the relative pronoun is the subject in its own clause (who killed) and should therefore be nominative.