The phrase "basketball player" refers to a profession or a category of people, rather than a specific individual.
We use the indefinite article "a" when referring to a general member of a group.
Thus, the correct sentence is:
"Kobe Bryant is a basketball player."
Thus, the correct answer is (A) "a".
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?