The correct answer is” has been living,” which is the present perfect continuous tense. This tense is used when an action started in the past and is still continuing in the present. ” Sam has been living in Bombay ever since his childhood.”
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?