The phrase "for the past three years" suggests an action that started in the past and is still continuing.
This requires the present perfect continuous tense: have/has + been + verb (-ing).
The correct form is:
"have been living" (present perfect continuous).
The correct sentence should be:
"They have been living here for the past three years."
Thus, the correct answer is Option A ("have been living").
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?